Improved summary when managing images

There are 2 problems with mass image operations.
1) When deleting image, shitty node_delete() spams user with messages. This is not only useless, it's annoying to see whole page full of "node blah blah was deleted" messages.
2) There's no nice summary of processed operations.

Attaching a patch which fixes this. We are going to use own function for deleting nodes, and we will track progress on each operation type and report it nicely on finish.