doc/strings update
A future "comanche UI" is going to need lists of available building blocks. Some of these are pretty easy to assemble, others are a bit more difficult and will have to go through a registration procedure. This checkin create such a registration procedure for page templates and their associated flavours and their assignable regions. The array itself is extensible since I don't know for sure at this stage what the front-end UI for this feature will ultimately require or even if there ever will be a front-end UI as this community still seems to believe that software writes itself and just magically appears, working perfectly.
missed the string update on an earlier checkin
Merge https://github.com/friendica/red into pending_merge