Update pyramid_redis_sessions required version.
Add time_zone model.
Set up lists of time zones.
Add time zone select template component.
Add time zone field to set up form.
Remove password minimum length from template.
Update builder model to handle time zone.
Correct error message.
Import TimeZone into __init__.py.
Add and update tests for time_zone.
Update set-up views to work with time_zone.
Split up model/meta.py.

Separate Base and DBSession so that Base can be imported without
creating a scoped session. And move the setting-up of the engine into a
more descriptive filename than meta.py.
Rewrite initializedb.py to use plain Session instead of scoped session.
Set up time zones table when initialising db.