Freeze MoSQL under 0.9.1 for Python 3 compatibility

See moskytw/mosql#38
Put requirement list into files
Bump supported minimum Django version to 1.6
Add coverage dependency
Remove deprecated commit_unless_managed() call
Fix warnings on tests

Remaining warnings are generated by django-nose and we can't do
anything about it until it releases the next version. :(

This also fixes compatibility with Python 3. Fix #9.
Fix database resolution when routers are in play

Fix #18