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
It's the same thing of calling the slot, but without creating a connection. Alternatively i could add a proper signal, connect it and emit when needed; It could make the reading of the code simpler