feat(gruntfile): add bowerRelease task to publish library on bower

I've created a new repository, http://github.com/caitp/angular-drop-bower,
where the bower release for this project will live. Updating it is automated
via the `grunt release` task, so that should hopefully be nice and easy.

All that remains is to add the new installation instructions to the demo page
and website, horray.

Closes #43