Remove cucumber tests in favor of vanilla integration tests

The cucumber test suite was in sorry shape, and barely running. This moves to a more vanilla integration test setup. Some notes about this PR:

* WebMock is removed in favor of some simple stubbing
* RubyForge login removed since RubyForge is very dead
* Dependencies endpoint removed since bundler-api had taken it over long ago
* Test helpers cleaned up

Really, this PR is just...

![where_did_the_gold_go](https://cloud.githubusercontent.com/assets/12610/5310774/64ce3588-7c07-11e4-8cd7-06d4c09896ac.gif)