Add branch created/deleted Stash events for issue transitions

It would be very useful when creating a branch from JIRA to be able to automatically transition from "Open" to "In progress". We might also want to transition from "In progress" to "Reopened" if a branch is deleted without a pull request (for instance, if the branch was created in the wrong repository). I would imagine adding Stash events for when a branch is created or deleted to the issue transitions page would be the most straightforward and flexible way to accomplish this.