Moved the OSMesaDummy functions from GuiQt into their own, new module...

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.