### What is this PR for?
As more and more document pages are added, it's really hard to find specific pages. So I added searching feature to Zeppelin documentation site([jekyll](https://jekyllrb.com/) based site) using [lunr.js](http://lunrjs.com/).
- **How does it work?**
I created [`search_data.json`](6e02423f54/docs/search_data.json) which is used for docs info template. `lunr.js` combines all of the text from all of the docs in `docs/` into `_site/search_data.json`. It looks like below.

All the info are comes from [Jekyll YAML front matter](https://jekyllrb.com/docs/frontmatter/) variables. (i.e. title, group, description.. that's why I rewrote all docs' title and description.)
[search.js](6e02423f54/docs/assets/themes/zeppelin/js/search.js) will do this job using this data!
### What type of PR is it?
Improvement & Feature
### Todos
* [x] - Keep consistency for all docs pages' `Title`
* [x] - Add some overview sentences to all docs pages' `Description` section (this will be used as the result preview)
* [x] - Add apache license header to all docs page (some pages are missing the license header currently)
* [x] - Add LICENSE for `lunr.min.js`
### What is the Jira issue?
[ZEPPELIN-1219](https://issues.apache.org/jira/browse/ZEPPELIN-1219)
### How should this be tested?
1. Apply this patch and build `ZEPPELIN_HOME/docs` dir -> please see [docs/README.md#build-documentation](https://github.com/apache/zeppelin/tree/master/docs#build-documentation)
2. Click `search` icon in navbar and go to `search.html` page
3. Type anything you want to search in the search bar (i.e. type `python`, `spark`, `dynamic` ... )
### Screenshots (if appropriate)


### Questions:
* Does the licenses files need update? Yes, for `lunr.min.js`
* Is there breaking changes for older versions? no
* Does this needs documentation? no
Author: AhyoungRyu <fbdkdud93@hanmail.net>
Closes#1266 from AhyoungRyu/ZEPPELIN-1219 and squashes the following commits:
7ec8854 [AhyoungRyu] Modify 'no result' sentence
91b71a7 [AhyoungRyu] Remove Apache license header since JSON doesn't allow comment
34afd5d [AhyoungRyu] Add Apache license header to search_data.json
6784282 [AhyoungRyu] Minor search page UI update
0389d28 [AhyoungRyu] Make index.md not to be searched
9f1ba42 [AhyoungRyu] Disable enterkey press & change icon
bd4956a [AhyoungRyu] Add docs.js & search.js to exclude list in pom.xml
624b051 [AhyoungRyu] Add Apache license header to search.js
1381152 [AhyoungRyu] Fix search result skipping issue
6e775f5 [AhyoungRyu] Make pleasecontribute.md not to be searched
ee11136 [AhyoungRyu] Fix some typos
fa01299 [AhyoungRyu] Refine 'description' in some docs as @bzz suggested
da0cff9 [AhyoungRyu] Exclude lunr.min.js
36ba7f1 [AhyoungRyu] Add lunr.min.js license info
f6a05a6 [AhyoungRyu] Apply css style for the search results
68eb997 [AhyoungRyu] Attach 'Apache Zeppelin ZEPPELIN_VERSION Documentation: ' to title
d908c37 [AhyoungRyu] Add searching page
a951fa6 [AhyoungRyu] Add search icon to navbar
0688a79 [AhyoungRyu] Keep consistency all docs' front matter for the right search result
040f532 [AhyoungRyu] Add template for storing docs info based on jekyll front matter
0705bd6 [AhyoungRyu] Add js files: lunr.min.js & search.js
### What is this PR for?
After #1087 merged, a new docs `shell.md` was added. But in the docs website, still Shell interpreter link points to `pleasecontribute.html`. So I changed this link, applied TOC and added more descriptions.
### What type of PR is it?
Documentation
### Todos
* [x] - Change `pleasecontribute.html` -> `shell.html`
* [x] - Apply TOC(table of contents)
* [x] - Add more description to `shell.md`
### Questions:
* Does the licenses files need update? no
* Is there breaking changes for older versions? no
* Does this needs documentation? no
Author: AhyoungRyu <fbdkdud93@hanmail.net>
Closes#1138 from AhyoungRyu/improve/shell-docs and squashes the following commits:
69d567d [AhyoungRyu] Address @felixcheung feedback
fca76a6 [AhyoungRyu] Apply TOC to rest-credential.md
c8e988b [AhyoungRyu] Change docs group manual -> interpreter
a0bf1d5 [AhyoungRyu] Add shell.html to _navigation.html
### What is this PR for?
This PR is for supporting various Credential APIs for users.
### What type of PR is it?
Improvement
### What is the Jira issue?
https://issues.apache.org/jira/browse/ZEPPELIN-1023
### How should this be tested?
- to create credential information.
```
curl -XPUT -H "Content-Type: application/json" "http://localhost:8080/api/credential" -d '{"entity" : "e1", "username" : "user1", "password" : "testpass"}'
```
- to get credential information.
```
curl -XGET -H "Content-Type: application/json" "http://localhost:8080/api/credential"
```
- to remove credential entity information.
```
curl -XDELETE -H "Content-Type: application/json" "http://localhost:8080/api/credential/e1"
```
- to remove all credential information.
```
curl -XDELETE -H "Content-Type: application/json" "http://localhost:8080/api/credential"
```
### Questions:
* Does the licenses files need update? no
* Is there breaking changes for older versions? no
* Does this needs documentation? no
Author: astroshim <hsshim@nflabs.com>
Author: AhyoungRyu <fbdkdud93@hanmail.net>
Author: HyungSung <hsshim@nflabs.com>
Closes#1030 from astroshim/ZEPPELIN-1023 and squashes the following commits:
1b94ae1 [astroshim] Merge branch 'master' into ZEPPELIN-1023
a580476 [astroshim] erase comment code
0609931 [astroshim] update credentialsMap
0f503fd [astroshim] to fix ci
d0c2bac [astroshim] changed syncronizedmap to concurrenthashmap
7b2a7c5 [HyungSung] Merge pull request #7 from AhyoungRyu/ZEPPELIN-1023-docs
80d8a30 [AhyoungRyu] Add rest-credential.md to index.md & dropdown menu
f546532 [astroshim] add rest-credential document
26433f2 [astroshim] change using syncronizedMap.
9b2c1c9 [astroshim] add checking null and blank values in the putCredentials method.
0371701 [astroshim] add more credential apis.