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.
Now that rxjs is stable and the rxjs team follows semver, we can update and unpin the dependency safely.
From now on the Angular application/library developers are in charge of controlling the rxjs version as long as it's newer than 5.0.1.
closes#13561closes#13478closes#13572