* main.cpp: removed path checking and db loading
 * card database: merge card loading methods into a single one
 * settings cache: take care of returning safe paths for decks,
replays, etc..
 * main window: if db loading fails (eg. first run), propose to run
oracle

NSIS: propose to run cockatrice instead of oracle

Rework card database loading

 * Move carddatabase-related method out of deckeditor tab
 * Load cards in another thread and render them progressively
 * Optimize database reload after enabled sets change

Fix deck editor column width

 * removed the noCard hack.
 * getCard() no more creates cards instead of just returning existing
ones
 * Fix the “edit tokens” dialog.
 * PictureLoader: avoid trying to download twice the same card
 * PictureLoader: correct return of card background
 * AbstractCardItem: avoid recalculating card color at every paint

Use a different file to save custom tokens

Misc required improvements

 * Use nullptr;
 * Refactor CardInfoWidget to use CardInfoPicture and CardInfoText
instead of duplicating code;
 * Added CardInfo::getColorChar()
 * Fixed some potential crashes
 * removed dead code related to CardInfoWidget
 * Don't require a restart after adding a new custom sets file
 * Bump CMake requirements to 3.1

 * Removed remaining picture handling from card database and cardinfo
 * removed the “noCard object” hack

Workaround the two remaining issues, mostly fixing the “load deck”
screen in tab_game:
 * Only preload up to the first 300 cards of a deck;
 * don’t even bother trying to load card images if they’ll be shown
with width <= 10

Trying a 17k cards deck like the one proposed in #67 is still a no go,
mostly due to the cpu time used to create all the objects. Anyway, i
tested decks up to 8k cards and they works fine now (if you like to
wait while trice is loading them)..

+ Users can now enable/disable the mouse over card scaling.

+ refactored code
+ improved card border lines (black)
+ cards no longer have curved edges, this prevents card image corners
showing behind.
+ tapped cards now have better border lines

Drop CardInfo’s own pixmap caches; use QPixmapCache instead.
Use QPixmap references instead of pointers.
Being stored in QPixmapCache, all card images are now subjected to
QPixmapCache’s size limit

Cards now scale up by 10% when mouse over.