Provide command to set global app launch options

[boombatower]

A number of fixes or features can be toggled with launch options. A handy feature would be the ability to set common launch options for all apps.

For example enabling Mesa hud with something like (from Dota 2):

GALLIUM_HUD=\"fps,GPU-load,VRAM-usage\" GALLIUM_HUD_VISIBLE=false GALLIUM_HUD_TOGGLE_SIGNAL=10 %command% -console

All of these settings are found in: ~/.local/share/Steam/userdata/$USERID/config/localconfig.vdf. Before something like this can be done a proper vdf parser with read/write ability would probably be best. I am not sure how feasible something like that is in bash.