added prebuild class "Bitmap" needed for assignment from image, the interpreter proxy and (maybe eventually) bitblt
added prebuild class "Bitmap" needed for assignment from image, the interpreter proxy and (maybe eventually) bitblt

HPI-SWA-Lab/RSqueak,HPI-SWA-Lab/RSqueak,HPI-SWA-Lab/RSqueak,HPI-SWA-Lab/RSqueak