Log when roles and cookbooks change

There is no logging that I can currently find, to indicate who uploaded a cookbook, made a change to a node or role, etc.

All such changes should have a log entry somewhere, describing who make the change and at what time.

Very ideally, a diff of the change would be logged too, but we can currently work around that by keeping the files and such in a local VCS repository. This doesn't help changed to node and role definitions though.