[WIP] Add support for CSS encapsulation to transcluding components

WIP [DO NOT MERGE]

1. Extract ComponentCssLoader so it can be shared by ShadowDomComponentFactory and TranscludingComponentFactory.
2. Implement a simple CSS transformer similar to the one provided by Platform.JS. This is here for completeness. A more full-featured compiler will be submitted as a separate PR.
3. Rename EventHandler into ShadowBoundary.
4. Rename WebPlatform into WebPlatformShim and provide two implementations: one based on platform.js and the other one built into Angular.


TODO:
- [ ] Refactor ShadowDomComponentFactory#call and TranscludingComponentFactory#call.
- [x] Test ShimmingViewCache in isolation. At the moment it is tested indirectly. 
- [ ] Set up one set of tests for both shims. Similar how we test the two component factories. 
- [x] Fix #1300
It could be used, but since the library is generic and does more than we need, importing it adds 160Kb to the generated (and minified) JS file. So we should probably try to build something more tailored to our use case.