BREAKING CHANGES:
- `NgElement` merged into `ElementRef`
- `Compiler.compile…` returns `ProtoViewRef`
- `ViewContainer` uses `ProtoViewRef`s and `ViewRef`s.
- `ViewRef`/`ProtoViewRef` in renderer were renamed to
`RenderViewRef`/`RenderProtoViewRef`.
Related to #1477Closes#1592
Introduces angular2/src/core/compiler/ViewFactory which
extracts ProtoView.instantiate and replaces ViewPool.
Note: This is a work in progress commit to unblock other commits.
There will be follow ups to add unit tests, remove TODOs, …