BIM: Fix Arch_SectionPlane having incorrect display style upon init

Regressed from previous behavior - there was Arch's refactor and the
base element that `SectionPlane` was inheriting from was
`App::FeaturePython`, not `Part::FeaturePython`. This changes a lot, since
`Part::FeaturePython` has predefined color (black in this case), which
later on - during property set of `SectionPlane` in properties caused
skipping of preferred setup of color.

src/Mod/BIM/Arch.py

@@ -1201,7 +1201,7 @@ def makeSectionPlane(objectslist=None, name=None):
     from WorkingPlane import get_working_plane
 
     sectionPlane = _initializeArchObject(
-        "Part::FeaturePython",
+        "App::FeaturePython",
         baseClassName="_SectionPlane",
         internalName="Section",
         defaultLabel=name if name else translate("Arch", "Section"),