Don't create a VRF for every Workgroup

That doesn't make any sense.
Disallow DynamicInterface in static Range
Disallow StaticInterface in dynamic Range
Remove unneeded function import
StaticInterface.range returns None if not in Range
Print warnings and errors to stderr
Don't set the vrf field of DynamicInterfaces

It'll be gone in a few commits anyway.
Move Vrf deletion to dhcp_migrate

...since that's the only place we'll create Vrfs
Re-order migrations so ifaces can validate range
Delete lots of migrations

... in preparation for creating new initial migrations
Remove iface vrf fields; add initial migrations
Add ORM freeze thing to SystemKeyValue migration
Fix some broken tests
Require South>=0.8.1
Fix the last broken test
Slightly improve efficiency by not being stupid
Cleanup and fixes suggested by @akeym
Merge branch 'schema-and-migration-fixes'

Conflicts:
	cyder/migration/management/commands/dhcp_migrate.py