Corrected behaviour of viewer snapshot function. It is now possible to specify snapshot sizes up to 8192x8192 independently from the glwidget. Additionally a "keep aspect ratio" check box has been added.

git-svn-id: http://www.openflipper.org/svnrepo/OpenFlipper/branches/Free@9907 383ad7c9-94d9-4d36-a494-682f7c89f535