Cleanup: server image

This PR removes all the image jobs from server, into graph/. There is one exception: `image_delete` which still has a dependency on the daemon (to be fixed); that has been moved to daemon/.

All this work was done by @shykes. I simply resolved rebase conflicts and migrated tests.

Ping @crosbymichael @LK4D4 @unclejack @erikh
Because we are not checking errors returned from register we do not know if this refactoring is overwriting any jobs already registered with the same name throughout the code base.

Do you think we can check the errors from register?