Modified code to only save data when data is actually modified, removed redundant images, and indexed skins from zero.

Skin #1 (both 2D and 3D) were already present in default. I removed the duplicates from skins, and added the default image names ("player" and "character") to the skin list.

That left skins being numbered from two, which was even odder than numbering from one, so since I needed to rename the files anyway, I numbered them from zero this time.

Previously, the skin file was saved every time the user logs in. That seems unnecessary, so I modified the code to save the file only when the data actually changes.