[OpenSCAD] Add unit test framework to module

The OpenSCAD module did not have any unit tests. This commit adds the
basic framework (and two very simple tests). The framework is modeled
after the unit tests in the FEM module.

src/Mod/OpenSCAD/Init.py

@@ -32,6 +32,8 @@ openscadfilename = param.GetString('openscadexecutable')
 openscadbin = openscadfilename and os.path.isfile(openscadfilename)
 if openscadbin:
     FreeCAD.addImportType("OpenSCAD Format (*.scad)","importCSG")
+    FreeCAD.__unit_test__ += ["TestOpenSCADApp"]
+
 FreeCAD.addExportType("OpenSCAD CSG Format (*.csg)","exportCSG")
 FreeCAD.addExportType("OpenSCAD Format (*.scad)","exportCSG")