Add option to cut off path for used WADs

[Qwertyus3D]

It can be a part of Clean or Optimize fucntions. Just remove unneeded information about path of WAD locations from worldspawn properties, since only WAD names do matter.

So it will be more like halflife.wad;xeno.wad;liquids.wad instead of /my lovely Steam directory location/steamapps/common/Half-Life/valve/halflife.wad;/my lovely Steam directory location/steamapps/common/Half-Life/valve/xeno.wad;/my lovely Steam directory location/steamapps/common/Half-Life/valve/liquids.wad;

It also can be useful to display a list of used WAD names in Debug info widget. Can be handy if there are several WADs used (and maybe mark if some WADs are missed currently).