Adjust primary keys of phpbb tables to integer to fix relations

Django will make Foreign key columns to phpbb tables as integer.
PhpBB's primary keys are mediumint. MySQL won't add a foreign key
constrain for mismatching data types.

We change the primary keys of the tables we are interested in from
mediumint (3 bytes) to integer (8 bytes) to get automatic migrations
for django models with references to those tables.
comment SessionAuthenticationMiddleware to fix runserver

It seems to be a Middleware present in 1.7b2
Add foreign keys to phpbb tables, make dates optional
Add basic models for abcapp

...generated with `python manage.py makemigrations abcapp`.