Rails 4.2

This pull request shall only be merged after rails 4.2 was released and https://github.com/rails/rails/pull/17453 gets solved. I just opened it so we can run tests on travis.

This branch will be regularly updated and finally merged into master after Rails 4.2 got released.

**As Rails 4.2 is another release that is not backwards compatible, Alchemy 3.1 won't be either and will only address Rails 4.2**