Path: Add new Slot operation

New slotting operation:
- Accepts selection of up to two features.
- Selectable features include: faces, edges, and vertices.
- User may select a single face or edge, or a pair of features.
- The path may be extended at the start and end.
- The path may be reversed.
- The path may be altered to the perpendicular in some cases.
- A unique Slot icon is included.
- Includes simple collision detection with warning message.

src/Mod/Path/PathScripts/PathGuiInit.py

@@ -72,6 +72,7 @@ def Startup():
         from PathScripts import PathSetupSheetGui
         from PathScripts import PathSimpleCopy
         from PathScripts import PathSimulatorGui
+        from PathScripts import PathSlotGui
         from PathScripts import PathStop
         # from PathScripts import PathSurfaceGui  # Added in initGui.py due to OCL dependency
         from PathScripts import PathToolController