Allow changing of transition 'to' on edit

Wow this is an old one; must have been one of my first attempting to do tests :) Rereading wondering if its better just to close this given #59. Deleting a transition and creating it again really only typically means having to redo the permissions, but given its likely to happen while you are setting up a workflow, its likely you have not yet gotten to permissions yet in the first place. Feel free to re-open if disagreeing.