Move to latest Rails releases for 3.1.x - 4.1.x
Use Travis's default Bundler

Travis now runs Bundler 1.5.3 by default, so just let it go.
Merge pull request #406 from stevenharman/update-travis-configs

Update Rails and Bundler dependencies
Add a facade to more easily get token from request

If you wish to you Doorkeeper outside of a Rails controller you must dig
deep into the internals of Doorkeeper to extract a token from an
incoming request. I needed to do this, for example, in a custom route
constrait. This PR adds a small facade which makes doing this simpler.