Add pie charts to promdash

See title. Plz comment with anything I've missed, or additional functionality you would like like.

requested in #114 

@tomcz @juliusv @grobie @ohookins

Right now we still have `removeFrame` in `frame_ctrl.js` and `removeGraph` here, although the functions that close the modal do the same thing. How about consolidating them all into this function here and it could be just:

```
$scope.removeWidget = function() {
  $scope.$emit('removeWidget', $scope.index);
  ModalService.closeModal();
}
```