Create branches.rb.  Move branch related actions there.  Add new methods...

... for (un)protecting branches and creating new branches - which requires Gitlab 6.8-stable or newer. Added tests for new methods and fixed old tests looking for methods in old locations.

Was trying to follow the documentation breakdown here: https://github.com/gitlabhq/gitlabhq/tree/master/doc/api

I don't yet have Gitlab 6.8-stable so I wasn't able to test the creation of branches via the API.