Integrate ActiveJob / DeliverLater / GlobalID with Rails

WIP.
Well every time a new adapter is added or an adapter removed we have to:
- update the Gemfile
- update the activejob/Rakefile
- update activejob/README.md
- update the guides
- and of course delete /  add the adapter files for enqueueing and testing

Not very optional :). From the above we can remove most the README.md and point to the guides.