Added better support for custom card images

This improvement greatly simplifies the use of custom JPEGs instead of the default card images. Benefits include:

1) All custom art can be placed in a single folder, without having to figure out which set it would normally belong to (normally more bothersome for cards in multiple sets as user-defined set priorities also play a role).
2) Allows players to easily share custom JPEGs since they all go into a single, predefined folder whose location is independent of the independent set priorities of the players.

Added an additional check prior to the previous order-of-priority when determining which JPEG file to use for a card.

New order-of-priority:
1) <Pictures path>/CUSTOM/<Card name>.full.jpg
2) <Pictures path>/<Set code>/<Card name>.full.jpg
3) <Pictures path>/downloadedPics/<Set code>/<Card name>.full.jpg
4) Download JPEG and place in <Pictures path>/downloadedPics/<Set code>/<Card name>.full.jpg

If a card appears in multiple sets, the highest priority set (a user-defined ranking) is used.

Prior order-of-priority:
1) <Pictures path>/<Set code>/<Card name>.full.jpg
2) <Pictures path>/downloadedPics/<Set code>/<Card name>.full.jpg
3) Download JPEG and place in <Pictures path>/downloadedPics/<Set code>/<Card name>.full.jpg

The old line 133 (new line 134) was commented out as it did not seem to serve any purpose (JPEGS are not named as such).