Add ng-click and button type to scope filtering

* This addition gives the user an ability to specify a submit function
  so that it can be used as a normal button that does an action — may be
  update some attribute by fetching data from the server — and not just
  a form submit. This will make it act more like a normal HTML button.

* The button type can be set which gets parsed as a string.
Hi kgrz. I understand the idea, and thanks very much for the pull request. It seems that `ngClick` does not need to be added to the directive scope or to the template argument though . I forked your plunker to demonstrate: http://plnkr.co/edit/laiGgLpPaXIGmbLELpyN