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/drag_knife.py

@@ -0,0 +1,72 @@
+################################################################################
+# drag knife.py
+#
+# NC code creator for attaching Z coordinates to a surface
+#
+# Dan Heeks 26th April 2012
+
+import recreator
+dragging = False
+from kurve_funcs import cut_curve as cut_curve
+import nc
+import area
+
+################################################################################
+class Creator(recreator.Redirector):
+
+    def __init__(self, original, drag_distance):
+        recreator.Redirector.__init__(self, original)
+
+        self.drag_distance = drag_distance
+        self.path = None
+        
+    def cut_path(self):
+        if self.path == None: return
+
+        print self.drag_distance
+        self.path.OffsetForward(self.drag_distance, False)
+        
+        nc.creator = nc.creator.original
+
+        if self.path.getNumVertices() > 0:
+            v = self.path.FirstVertex()
+            nc.creator.feed(v.p.x, v.p.y)
+            
+        cut_curve(self.path)
+        nc.creator = self
+            
+        self.path = area.Curve()
+        
+    def feed(self, x=None, y=None, z=None, a=None, b=None, c=None):
+        px = self.x
+        py = self.y
+        pz = self.z
+        recreator.Redirector.feed(self, x, y, z, a, b, c)
+        if self.x == None or self.y == None or self.z == None:
+            return
+        if px == self.x and py == self.y:
+            return
+            
+        # add a line to the path
+        if self.path == None: self.path = area.Curve()
+        self.path.append(area.Point(self.x, self.y))
+        
+    def arc(self, x=None, y=None, z=None, i=None, j=None, k=None, r=None, ccw = True):
+        recreator.Redirector.arc(self, x, y, z, i, j, k, r, ccw)
+        
+        # add an arc to the path
+        if self.path == None:  self.path = area.Curve()
+        self.path.append(area.Vertex(1 if ccw else -1, area.Point(self.x, self.y), area.Point(i, j)))
+
+def drag_begin(drag_distance):
+    global dragging
+    if dragging == True:
+        drag_end()
+    nc.creator = Creator(nc.creator, drag_distance)
+    dragging = True
+
+def drag_end():
+    global dragging
+    nc.creator.cut_path()
+    nc.creator = nc.creator.original
+    attached = False