Add pricing from deckbrew.com (refs #147)

* the previous PriceUpdater class has become abstract
* BLPPriceUpdater inherits the old code for blacklotusproject.com
* DBPriceUpdater is a new implementation for deckbrew.com
* add a setting to choose between the two
Can you make this an enum?

Also add a default case so that someone can't break it by messing with their settings file