fix(tagging compiler): a text child after a directive child
test(ng-class): Make the ng-class tests compiler agnostic

A better place for this logic may be JQuery.
See #759
feat(compiler): Make the TaggingCompiler the default compiler
chore(pubspec.lock): upgraded route_hierarchical to 0.4.15
chore(CONTRIBUTING): merge relevant updates from Angular.js

Port changes to Angular.js CONTRIBUTING.md since AngularDart version
was forked.

Closes #748
fix(animation): correct broken build http://dartbug.com/17634
fix(scope): allow concurrent fire/add/remove on listeners
fix(forms): ensure models are validated when validator attributes change
fix(NgModelValidators): ensure all validators can properly toggle attribute values
chore(forms): cleanup unused code