Standalone Selection Menu

[frostworx]

Based on the recently added metadata auto creation I'm going to also add a "Standalone Selection Menu",
which can be launched without steam and automatically lists all installed steam games with game id and name
(a dynamically changing game picture would be nice, but I don't know if yad can handle this)
The minimal function would be to open the settings menu for the selected game, but other options are possible as well.
Another possible feature would be the option to start a selected game totally without steam (maybe filter games without a bundled steam_api64.dll)

The metadata files are auto generated if not available and updated when the last update is older than 24hrs or on demand.

[frostworx]

Basically added with 84a6359
Maybe expand later