Sync classes

[w33ble]

Keeps the $control classes synced up with the $input.

This is especially useful when using the Bootstrap 3 theme.

With this change, users can apply styles to the input on .ng-dirty.ng-invalid like this, for example:

input.ng-dirty.ng-invalid,
textarea.ng-dirty.ng-invalid,
select.ng-dirty.ng-invalid,
.selectize-input.ng-dirty.ng-invalid {
  border-color: @state-danger-bg !important;
}

[w33ble]

No idea why the tests are failing - the same tests fail on master too, so it's related to the changes I made...

[w33ble]

I figured out the test failing issue - see #28