add missing default textures

[ScanMountGoat]

It should be possible to access all the textures from the default textures folder. These can be hardcoded rather than loaded from images for simplicity.

• [x] add missing textures
• [ ] generate textures at runtime

[zrksyd]

This should be closed. (Unless, you'd rather the textures be hardcoded rather than load from images.)

[ScanMountGoat]

I'm leaving this open since it's only partially implemented.