[WIP] Rails 4 upgrade

**DO NOT MERGE YET, WORK IN PROGRESS!**

To get some first feedback I'm already creating this pull request. Of course we will cleanup the commits when it's done for merging.

There will me multiple barclamp pull requests linked against this pull request.
Generally speaking, there are some bits in there that I think we should change for easier debugging while we are doing milestones (raise_on_missing_translations, for instance). Do you think it's best done in the package?