Fix saving theme

Fix saving theme

The option -trueColors is now saved with the theme settings when a
pieceImageDirectory was given in XBoard, and the piece colors are
saved when this option is off even with a piece directory. The square
colors are now also saved when useBooardTextures is on, but the textures
are transparent. For this the transparency also had to be made visible in
the WinBoard front end, (by moving the flags for it to backend.c), but
always stay at the default 0 there.