trac: Allow accepted -> new

[Elrond]

In some cases, one wants to go back to "new":

• Maybe one was going from new -> accepted by accident.
• Some tickets have been so long in accepted, that they need a re-evalaution. (One could ask for yet another state, but I tend to like less states, and more tags)

I don't know, whether other states need to be able to go directly to new also. I doubt it. In the worst case, one can go to accepted first and then to new.

• review: Really, there is a patch, it should be looked at. If things are unclear, maybe first go back to accepted or in_progress.
• in_progress: There is something happening. If not, well, go back to accepted first.

[Elrond]

If this is resolved, please more #254 to new.

[Elrond]

Okay, the workflow can't be changed on the webif by trac_admins. It has to be done on trac.ini. As cwebber is busy, maybe simonft finds the time?