Extensive Path Workbench improvements.

Implement libarea improvements for profile
Implement libarea pocketing.
consolidate occ and libarea pocketing operation into one with algorithm
switch
consolidate occ aand libarea profile op into one with algorithm switch
add basic engraving operation.
Add rough UI for profile holding tags
implement holding tags for libarea profile.
implement basic defaults for depth settings.
First move in Drilling is rapid to clearance height.

UI needs lots of work but is usable.

src/Mod/Path/PathScripts/nc/hpgl2dv.py

@@ -0,0 +1,22 @@
+# hpgl2dv.py
+#
+# Copyright (c) 2009, Dan Heeks
+# This program is released under the BSD license. See the file COPYING for details.
+#
+
+# This is the same as the hpgl2d machine, but uses units of 0.25mm instead of 0.01mm
+
+import nc
+import hpgl2d
+
+class Creator(hpgl2d.Creator):
+    def init(self): 
+        hpgl2d.Creator.init(self) 
+
+    def imperial(self):
+        self.units_to_mc_units = 101.6 # multiplier from inches to machine units
+
+    def metric(self):
+        self.units_to_mc_units = 4 # multiplier from mm to machine units
+
+nc.creator = Creator()