Fixed Runner.default_path.
Add GObject.threads_init calls where needed.

This was necessary in order to improve the performance of
Lutris on SteamOS. Downloading and installing games was ridiculously
slow before.
Fixed game config saving for AddGameDialog.
Avoid KeyError in vice
Remove duplicate vice executable
Fix manual game adding
Deprecate constants module
Runner no more required in game's config
Set LD_LIBRARY_PATH when configuring snes9x
Avoid launching game twice
Get rid of realname and runner in configs
Avoid launching or installing twice the same game
Test manual game creation