perf(ngModel): change ng-model/form controllers to use prototype methods

BREAKING CHANGE:
The use of prototype methods instead of new methods per instance removes the ability to pass NgModelController and FormController methods without context.

For example `$scope.$watch("something", myNgModelCtrl.$render)` will no longer work because the `$render` method is passed without any context. This must now be replace with `$scope.$watch("something", function() { myNgModelCtrl.$render(); })` or possibly by using `Function.prototype.bind` or `angular.bind`.

Author: jbedard