snes9xgx, fceugx and vbagx with screenshots support

I have spend a few days adding some small features to this emulators that I was missing.

- screenshots preview, when selecting a game you'll be able to see an screenshot of it. It seems that everybody is more intereset on game cover, but for me this is a better option
- when entering a 7zip folder it will store the last game played (this only happened oustide 7zip folders)
- when leaving a folder (normal folder or 7zip) the current one will be automatically selected (very useful when you have been playing Zool and don't want to start searching again from 3x3 eyes)
- when showing the contents of a 7zip folder the main filename will be stripped and only the rom info showed (the text scroll is good, but most of the filenames are way too long and the important info is really at the end)

you can find my original post and the link to the emulators on gbatemp forums