Add feature to run commands after gamelist generation

[tobiasger]

I think it would be nice to be able to run custom scripts/commands after the game list generation process is done. And probably also after the caching is done. With that, I mean to be able to add the path to a script or a command to run as soon as the process fires some kind of event that it's finished. Similar to how you can run a video convert command with the videoConvertCommand setting.

There is a problem with adding colons to the launch command for Pegasus, if I for example have the emulator running on Windows and want the path to start with "C:/", and I think it would be nice to for example be able to run a search and replace script that would correct the missing semicolon from all generated metadata files, as an use case example.

[muldjord]

I decided to look into the problem with : and ended up simply removing the code that removes them. Everything still seems to work so... 3.7.5 released where : is now allowed.

[tobiasger]

Great @muldjord! I know that you don't support the Windows version of the software, but will this find it's way to a Windows release eventually?