Move all book-related images under "img"

Also:
 * use the "absolute path" syntax as used in the rest
of the image locations
 * png files are no longer required since we use svg for
   the web version and convert to PDF for the PDF version
A referenced file no longer exist --> commented out.
Move all purely website related images under "images"

Also corrected all references.

 * `favicon.ico` existed multiple times -> use the one under images
   (also corrected path in the `conf.py`)
 * also moved `white_wall_hash.png` although this is not
   referenced anywhere and might just as well be removed completely.
Make sure the build dir exists before copying something there.
Forgot to update one image reference.
Adds some PDF metadata. Might get tweaked still.
Merge pull request #204 from dietmarw/cleanUpImageLocations

Clean up image locations