Moved the OSMesaDummy functions from GuiQt into their own, new module OSMesaDummy.  Having the dummy OSMesa functions in GuiQt did not work for linking on all systems.  As mentioned in a previous commit, the dummy OSMesa functions are needed to prevent OpenGL 'clashes' now the the 'wb_command -show-scene' command is used in Workbench as part of the Help System.