chore(change detection): fix a typo in toString()
fix(NgModelValidators): ensure that number input types render invalid when non-numeric characters are present

input[type="number"] treats non-numeric values as NaN values and these are considered valid when
double.parse is used. This commit fixes the validation for the model to properly address the
invalid number when a NaN value is detected.
feat(forms): introduce the control.hasError helper method
style(animate demo): code cleanup
refactor(change_detection): remove unnecessary conditional expression

`prev` is guaranteed to not be null here, the method would throw noSuchMethod if it were.
fix(forms): do not reset input fields on valid submission
chore(docs): fix typos
chore(doc): build docs for angular/angular.dart repo only
fix(readme): Readd the Travis badge
fix(template_cache_generator): support traversal of partial files

Fixes #662