Cleanup feature

[oherau]

Most games where made for a specific target machine or OS, so in addition to core data and resources they include many files which are useless for ScummVM engine to run the game.
Sometimes reeditions also include bonus files such as Windows fonts, posters, and wallpapers.

It would be nice to have a clean-up feature allowing to remove useless files (such as *.EXE, *.BAT, *.PDF, Exe Binaries, etc.) and/or keep only resources required by the game itself.

A file with starting codes might be kept in the game directory, so a warning message should be displayed before any cleanup, with a cancel option.