Reshuffle texture files

Some texture files are added, providing both ETC1 (in .ktx format)
and DXT1 (in .dds) format versions for all textures. One is renamed.
Some unused ones are deleted.

Signed-off-by: Harm Hanemaaijer <fgenfb@yahoo.com>
Create texture creation functions and use them for player sphere

Create functions to create simple checkboard or stripe textures
using selected colors.

A striped texture is used on the player (control object) spere,
giving a much better sense of movement.

Signed-off-by: Harm Hanemaaijer <fgenfb@yahoo.com>