Every time the InvoluteGearFeature python module was imported, and we're
in GUI context, the command "PartDesign_InvoluteGear" was registered. On
the 2nd (3rd, ...) time, this was reported as an error in the console,
like "error: Command.cpp(1841): duplicate command PartDesign_InvoluteGear"
The first import happens when the PartDesign FreeCAD Module is loaded,
via `InitGui.py`. Subsequent imports may happen when e.g. executing the
involute gear command or when running it's tests via FC's Test WB.
This change now registers the command only then the PartDesign WB is set
up in InitGui, not when importing the python module. The same fix is
applied for sprocket, where the same pattern for command registration
was used.
In addition, the import error catch was removed, which seems to be a copy
paste left-over from the ShaftWizard. In contrast to ShaftWizard,
involute gear and sprocket only use modules from the Python standard lib,
so I think this precaution is not worth the additional complexity, just
for hiding actual errors.
A hole feature is something needed, however, the current implementation does not use the attacher code which would made it intuitive and compatibel to other workbench tools. A reimplementation is needed.
