Feature: Allow several users to administer a repository together

Hi James,

we are using gitblit in our company. People really like to have a hosted gitblit alternative in-house. But after a few months, we have a couple of feature wishes now. One is to allow several users to administer a repository together. Projects are really self-organized. They would like to give a new project member access rights to their central project repos instantly even if the repo owner is out of office at the moment.
If you like the idea, feel free to merge this into the gitblit/master.
If you have any further change requests before this can be merged into the master, just let me know.

Best regards
Sarah