[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.
Hrm, given the amount of issues we generally have, I'd like to keep this to `:debug` even for production right now. What do you think?