Pruning balena registry stored images

@MBer you should see a little delete button (trash can icon) on the right hand side of releases - is this not appearing for you?

@drcnyc No, but I found that the ui container still had code from before the latest commit there. open-balena-admin/scripts/compose pull was required to get the latest images before launching the containers again. Everything works now, and the changes are all useful for deletion management:

The bulk-select is nice too:

Deletion confirmed working (clicking Confirm in the pop-up twice per batch). Thank you very much!

@MBer no problem, glad you were able to make use of it! Remember to run garbage-collect on your registry periodically to free up the storage after deleting releases.