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
The QUrl::QUrl(const QString &) constructor assumes the string is human-readable, and automatically percent encodes all characters that are not allowed in a URL. The code is a bit lame anyway, most a copy/paste of the existing one for blacklotusproject.com