AVALANCHE: Implement MainMenu::option().

Rework and implement a lot of connected functions.
AVALANCHE: Fix parentheses in Help::handleMouse().
FULLPIPE: Implement scene19_updateCursor()
FULLPIPE: Implement scene18_setupSwingers()
AGOS: Correct typos in comments.
AGOS: Update debug tables.
VOYEUR: Some cleanup related to the onOff and pick masks
VOYEUR: Fix memory leak when quitting in showTitleScreen()
VOYEUR: Invert check on getBoltGroup in getComputerBrush for consistency