chore: Coveralls Integration

Anyone can figure out how to configure [coveralls code coverage](http://coveralls.io)???
I have been trying on a [branch I created](https://github.com/thgreasi/ui-sortable/tree/coveralls) but with [no luck](https://coveralls.io/r/thgreasi/ui-sortable)...

@douglasduteil Could we also normalize the coverage configuration into angular-ui-publisher (hope this does not sound stupid)?
