Currently, core depends on DomRenderer, which depends on the browser.
This means that if you depend on angular2/core, you will always
pull in the browser dom adapter and the browser render, regardless
if you need them or not.
This PR moves the browser dom adapter and the browser renderer out of core.
BREAKING CHANGE
If you import browser adapter or dom renderer directly (not via angular2/core),
you will have to change the import path.
