TypeScript compiler will now build to ES2015 code and modules. Babili is used to minify ES2015
code, providing an initial optimization that we couldn't previously get just from Uglify. Uses
Babel to convert ES2015 to UMD/ES5 code, and Uglify to minimize the output.
the bundles have source mpas disabled for now because when we downlevel
the esm bundle to es5 tsc doesn't consider the original source map so
we end up with a source map pointing to the esm bundle instead which is
not useful.