Use ng-click instead of ng-submit.

According to the form directive documentation, using ng-submit while
having more than one field and one or more buttons with ng-click set
causes the framework to submit the form as soon as a button with
ng-click is hit.

Also:
* AddMovieController
    * Rename $scope.processForm to $scope.submit
    * Rename deleteMovie to _deleteMovie
    * Move _deleteMovie outside the if block.
    * Correct the alias for API_URLS in _deleteMovie. It must be URLS.
* MovieDetailsController
    * Correct API_URLS attribute. It says movie instead of movies.