It's just listing directories of a mod for now, but should give some
idea what the mod changes.
Also moved some functionality from pathman to modman.
Mods added with the `-mod` parameter are now managed by modman.
Moved list of mods logic to a new CModManager class.
The list of enabled mods is now managed by a flag instead of directory
names of mods.
Mods are now disabled by default.
Also general cleanup, fixing issues from the code review in
https://github.com/colobot/colobot/pull/1191 and fixing linter issues.
Regression: the state of enabled/disabled mods is now not persistent.
The plan is to use some kind of config file for this.