Add a configuration allowing the deletion of tickets

[roded]

I'm not sure if a positive decision was made to disallow deleting tickets in gitblit. Either way, the ability to delete tickets (whether out of the box or enabled via configuration) would be quite useful especially in projects with quite a bit of noise coming from many users. Not to mention the satisfaction of various OCD-like tendencies :)

[gitblit]

I think adding a delete ticket function is probably a good idea. Maybe it should be enabled by a setting, although that isn't my first thought.