Add a large number of texture images

Add a large number of texture images

Many plain textures that can be arbitrarily cut are provided in a basic
texture package. A naming convention is applied to sensibly group them
in the browser, the names starting with 'wood', 'stone', 'vinyl' etc,
and ending on a rough color indcation.
 In a subdirectory 'patterned' there are a number of 1x1 images that will
be scaled by XBoard to cover exactly a single square, to be sure all
squares display the same pattern (for which these images are designed).
 A Makefil can be used to install, or create a distribution tar ball.