fix(scope): remove GC pressure created by watchCollection getter
chore(docs): Correct README.md links

The StackOverflow link refers to none existing tag angulardart.

Change the link so it links to the existing angular.dart tag
chore(import): Make test/tools/* not depend on dart:html
fix(ng_model): do not save/restore selection unnecessarily

Closes #264
chore(cleanup): analyzer warnings