Add pricing from deckbrew.com

* 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
use a signal instead of calling QMetaObject::invokeMethod
Create an enum for price sources

Probably settingscache would have been the correct place for the enum,
but keeping it in the same class/file where price sources are defined
sounds cleaner to me
Added default cases to switch
Ensure all card prices are retrieved correctly

Query card database to get a multiverseis for a card.
Get card price using that id instead of card name.
Tested Aether, split cards, question elemental?, _____
Updated for new API

 * Use the new, shortest API m=
 * for a card, grab prices for all sets
 * use the lower price for a card from all sets, but avoid prices=0
(e.g.: some M15 cards have no price yet)
Merge remote-tracking branch 'upstream/master' into master_feature_prices
Merge branch 'master' into master_feature_prices
Ensure the whole table gets refreshed when updating prices
Split price retrieval on multiple request
small fix: moving the url length check in the inner loop
Merge pull request #152 from ctrlaltca/master_feature_prices

Add pricing from deckbrew.com (refs #147)