fix(ngModel): do not dirty the input on $commitViewValue if nothing was changed

Calling `$commitViewValue` was was dirtying the input, even if no update to the view
value was made.
For example, `updateOn` triggers and form submit may call `$commitViewValue` even
if the the view value had not changed.

Closes #7457
Closes #7495
docs(tutorial): fix link to bower in step 12

Muchas gracias! \o/

Closes #7507