Add flup to the requirements

Added flup to the production requirements file
Alter config.py

Fixed config.py to run locally with sqlight. Pool size and timeout
settings will break sqlight initialization. Set MySQL specific settings
to be None in order for this to work.
Fix runserver.py

Fixed runserver ``app`` import to work.
Add Slet model

Added test model for abstract entity Slet. This will probably be removed
sooner or later