Remove coveralls and some duplicated files in the gem structure

I got rid off coveralls (already removed the badge on master, sorry should have been in this PR) as for weeks at least it displayed the wrong test coverage on the badge... I believe code climate coverage is still sometimes a bit faulty but it shows the correct overall percentage.

During my quest to remove it I noticed some duplication in the new gem structure that I tried to get rid off:

* the `code_coverage` now resides in a top level `spec` folder that I thought was ok to create now due to the imo brilliant idea of @jasonrclark in #1000 to have a spec_helper there
* I removed the Gemfiles in the sub gems as they duplicated the major one on the top level

If any of those had a purpose I just didn't understand, I'm happy to reset/revert :)

Yes I'm really a DRY person :)

Tobi