Remove dependencies on contracts

[dafeder]

There are a number of pieces of DKAN's codebase that live in external libraries that provide little value outside the DKAN context. These include the "contracts" interfaces, the procrastinator library, and the locker (which doesn't appear to be in use). (This also may include RootedJsonData but we will address that in another issue.)

To the extent possible, remove these dependencies and move any classes still needed into the DKAN project.