PD: Add tests for InvoluteGear

There are some basic tests to cover the gear profile and its parameters
and some integration tests for the interaction with PD Pad and Pocket.

I followed the same pattern as the other PartDesign tests, e.g. not using
PEP8 style method names. Eventually some helper methods could be
extracted and moved to the common base framework in Mod/Test, but that's
another step.

src/Mod/PartDesign/TestPartDesignApp.py

@@ -48,3 +48,6 @@ from PartDesignTests.TestFillet import TestFillet
 from PartDesignTests.TestChamfer import TestChamfer
 from PartDesignTests.TestDraft import TestDraft
 from PartDesignTests.TestThickness import TestThickness
+
+# extras
+from PartDesignTests.TestInvoluteGear import TestInvoluteGear