Ability to remove yourself from repositories, inactive repos, and repo dropdown sorting (BB-138)

(Based on convo from IRC with jespern)

You should be able to remove yourself from a repositories' access list if you are not the owner. Currently, if you're on any active repos, it's very easy to build up an absolutely huge list of forks, including ones that are already done and won't get touched again.

In addition, the ability to mark a project inactive would be very useful; This would remove it from the repo dropdown, and maybe prevent anybody from pushing to the repo until it is marked active again.

Finally, the repo dropdown should be sorted by something like "following, username asc, reponame asc".