Linking resources to Commits - make every resource traceable

[joepio]

In the current implementation of atomic-server we can find all versions of a resource by visiting the /all-versions endpoint. It works pretty well, but it is not discoverable. Also, it requires performing a search query on the back-end. This can be optimized, of course, but having an explicit link to a resource is more elegant and will also be performant to others.

One alternative way of doing things, is adding a previous-commit property to every resource after applying the commit. With this property, it becomes easy to find the commit, and with that, also the last editor, the edited date.. And if these commits also link to previous commits, we can quickly find the first commit!