Auto-detect and set resolution on first run (#1568)

**(Do not merge yet.)**
Implements a fix for issue #1568. Automatically sets the game's resolution to that of the desktop the first time the game is run.

Looks for a value corresponding to the 'LatestBackground' setting in order to determine if the game has been run before (as 'LatestBackground' does not have a default value and is set when the game is first run).

Destroys and re-initializes the engine to force the change without restarting.