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?, _____

* 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

Ref #112

"The price tag feature currently has two bugs.
1. The final price that a card ends up with is the one in the last set
alphabetically, instead of the one from the set with the lowest price.
2. Black Lotus Project sometimes gets in prices for cards from Masters
Edition, for some reason. This set only exists in Magic the Gathering:
Online, i.e., not physically, and should not be considered. This might
be considered a BLP bug and not a Cockatrice bug.

This patch fixes those two bugs. I also changed the price value to be
based on BLP's "price" value instead of the "average" value. Seems more
logical."

Signed-off-by: Daenyth <Daenyth+git@gmail.com>

Converted PriceUpdater from QScriptEngine to Qt-Json. I don't feel comfortable running unchecked JS code from an external source.

price is dispay in both places.