Stand-alone code: Blank the whole canvas (fixes #248)
Stand-alone code: Blank the whole canvas (fixes #248)

venkat24/codeworld,venkat24/codeworld,alphalambda/codeworld,three/codeworld,stefan-j/codeworld,three/codeworld,tgdavies/codeworld,google/codeworld,tgdavies/codeworld,alphalambda/codeworld,pranjaltale16/codeworld,parvmor/codeworld,venkat24/codeworld,stefan-j/codeworld,parvmor/codeworld,stefan-j/codeworld,google/codeworld,alphalambda/codeworld,parvmor/codeworld,nomeata/codeworld,tgdavies/codeworld,pranjaltale16/codeworld,nomeata/codeworld,three/codeworld,nomeata/codeworld,google/codeworld,pranjaltale16/codeworld