cmake: cleanup around qt 3D viewers
- separated compilation of QtViewer & QGLViewer
- QtViewer is no longer a dependency to a lot of projects

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@9715 b7f1a160-662a-0410-a6d8-bea165342f16
fix image and Flexible : bug in branching images

git-svn-id: svn://scm.gforge.inria.fr/svnroot/sofa/trunk@9716 b7f1a160-662a-0410-a6d8-bea165342f16