Added save and load feature to AutoUV texture shader

[Micheus]

It was necessary to apply the filename:nativename/1 in the wings_image:find_image/1 in order to get the correct file format for comparison. It was also made two fixes:

• a crash introduced with the use of string:casefold/1 which doesn't handle 'none'. It can happen when a new image for texture was just created;
• a crash when an OpenGL error is fired and the text formatting in the message was not in accord with the parameter type.

NOTE:

• Added option to save and load texture settings in AutoUV window. Texture settings can now be reused for other projects.

[Micheus]

@dgud, it's rebased with the current master - just in case you consider to give it a try.