This commit adds a forum tree YAML file (URL-based rather than an
actual tree...) and the 'forums' and 'create-forums' commands for
the master script.
A page /admin/forums is also used to currently display the forum
tree, although this will probably be turned into a full table with
forum descriptions, and a form with edition capabilities.
First migrate without the foreign key to create the tables, then add the
foreign key in a second migration.
Also removed unneeded imports that caused dependency cycles.
Minor "style" edits with the ambiguous use of super and unnecessary
db.Model inheritance.
Darks
Lephe