En Masse change deletion

[Kevin Ballard]

Despite not being the original intent, TicketDeletionPlugin is my primary means of deleting ticket spam. At the moment, though, I have lots of spam that I need to clean out, as in lots of spam changes on a single ticket. I would really like the ability to delete changes en masse instead of individually, via simply a checkbox next to each change rather than the 2 buttons, and then have the 2 buttons at the bottom to delete all marked changes.