Add config overrides from env variables

For now this simply allows loading a different db uri, but can be used
for loading any non-standard config value for testing.
Add processed scale column to Card model

By saving the scale with the card, it doesn't need to be passed around
everywhere in the app.  This should simplify all of the translations
littered around the various controllers/views.
power and toughness parsers correctly handle non-creature cards

Much like loyalty now checks card type, power and toughness return
None for cards which are not creatures.
Controller update - pass card type to pow/tough, save card scaling

power and toughness now check card types for creature, and the scale
factor used to calculate processed fields is saved with the card.
Overhaul card db converter

Now properly patches the app's database location and saves the
calculated rows in a new database.  Overwites any existing db in
the output location.