Enabling the moderators_manage_categories_and_groups site setting will allow moderator users to create/manage groups.
* show New Group form to moderators
* Allow moderators to update groups and read logs, where appropriate
* Rename site setting from create -> manage
* improved tests
* Migration should rename old log entries
* Log group changes, even if those changes mean you can no longer see the group
* Slight reshuffle
* RouteTo /g if they no longer have permissions to view group
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
