Add different compare methods for sorting

Give DeckList nodes the ability to sort based on name, price, or
number.
Allow sorting on different columns
Sort correctly when adding cards
Fix GUI glitches when adding cards to a deck

Since we no longer sort on just card names, we need to emit updates
for the parent of the card we add.
Clean up DecklistModel::addCard()

Split common functionality out of the if-else block.
Oracle: build with qtjson
OracleImporter: use json to parse cards in sets

Problem: Split card are imported as 2 different cards; need to find
some way to join them
Corrections to sets.xml for mtgjson.com

 * Used http://www.woogerworks.com/files/sets.xml as a base
 * update version
 * use mtgjson.com as source
 * adapted some sets name (es: 6E => 6ED)
Caveats:
 * Not all previous sets are present (e.g.: WOTC, WMCQ, WRL); they were
not present in woogerworks’s sets.xml anyway
Fix import of P/T; misc optimizations
Use mtgimage.com for card images
Keep gatherer as image source; mtgimage as a hq alternative
Oracle: build with qtjson
OracleImporter: use json to parse cards in sets

Problem: Split card are imported as 2 different cards; need to find
some way to join them
Corrections to sets.xml for mtgjson.com

 * Used http://www.woogerworks.com/files/sets.xml as a base
 * update version
 * use mtgjson.com as source
 * adapted some sets name (es: 6E => 6ED)
Caveats:
 * Not all previous sets are present (e.g.: WOTC, WMCQ, WRL); they were
not present in woogerworks’s sets.xml anyway
Fix import of P/T; misc optimizations
Use mtgimage.com for card images
Keep gatherer as image source; mtgimage as a hq alternative
Merge branch 'mtgjson-importer' of https://github.com/ctrlaltca/Cockatrice into mtgjson-importer
Merge splitter cards into a single card
Import data from mtgjson's allsets.xml

* add multiverse id to cards.xml
* remove pictures urls from cards.xml
TBD:
* fix/clean oracle’s gui
* add support in cockatrice