added GetSize call to renderer, this returns the size of the actual render area (which is normally smaller ten the window size)
added GetSize call to renderer, this returns the size of the actual render area (which is normally smaller ten the window size)

git-svn-id: 83c4c97093aeea62ac982fbfd516bf9db27f5c99@1831 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok