Summary:
This was a little bit of an invasive change with the display handler, but I think that this is the right call. When sending display events for objects, we should account for the supplementary view as part of the section controller. This is especially useful for headers and footers.
Note that this wont effect the working range API at all.
Fixes#300
Closes https://github.com/Instagram/IGListKit/pull/470
Differential Revision: D4551338
Pulled By: rnystrom
fbshipit-source-id: dda6fbf18bcfc2c941d80ee2314a543d1ab83843