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/hxml_writer.py

@@ -0,0 +1,130 @@
+import tempfile
+
+class HxmlWriter:
+    def __init__(self):
+        self.file_out = open(tempfile.gettempdir()+'/backplot.xml', 'w')
+        self.file_out.write('<?xml version="1.0" ?>\n')
+        self.file_out.write('<nccode>\n')
+        self.t = None
+        self.oldx = None
+        self.oldy = None
+        self.oldz = None
+
+    def __del__(self):
+        self.file_out.write('</nccode>\n')
+        self.file_out.close()
+
+    def write(self, s):
+        self.file_out.write(s)
+
+############################################
+
+    def begin_ncblock(self):
+        self.file_out.write('\t<ncblock>\n')
+
+    def end_ncblock(self):
+        self.file_out.write('\t</ncblock>\n')
+
+    def add_text(self, s, col, cdata):
+        s.replace('&', '&amp;')
+        s.replace('"', '&quot;')
+        s.replace('<', '&lt;')
+        s.replace('>', '&gt;')
+        if (cdata) : (cd1, cd2) = ('<![CDATA[', ']]>')
+        else : (cd1, cd2) = ('', '')
+        if (col != None) : self.file_out.write('\t\t<text col="'+col+'">'+cd1+s+cd2+'</text>\n')
+        else : self.file_out.write('\t\t<text>'+cd1+s+cd2+'</text>\n')
+
+    def set_mode(self, units):
+        self.file_out.write('\t\t<mode')
+        if (units != None) : self.file_out.write(' units="'+str(units)+'"')
+        self.file_out.write(' />\n')
+        
+    def metric(self):
+        self.set_mode(units = 1.0)
+        
+    def imperial(self):
+        self.set_mode(units = 25.4)
+
+    def begin_path(self, col):
+        if (col != None) : self.file_out.write('\t\t<path col="'+col+'">\n')
+        else : self.file_out.write('\t\t<path>\n')
+
+    def end_path(self):
+        self.file_out.write('\t\t</path>\n')
+        
+    def rapid(self, x=None, y=None, z=None, a=None, b=None, c=None):
+        self.begin_path("rapid")
+        self.add_line(x, y, z, a, b, c)
+        self.end_path()
+        
+    def feed(self, x=None, y=None, z=None, a=None, b=None, c=None):
+        self.begin_path("feed")
+        self.add_line(x, y, z, a, b, c)
+        self.end_path()
+
+    def arc_cw(self, x=None, y=None, z=None, i=None, j=None, k=None, r=None):
+        self.begin_path("feed")
+        self.add_arc(x, y, z, i, j, k, r, -1)
+        self.end_path()
+
+    def arc_ccw(self, x=None, y=None, z=None, i=None, j=None, k=None, r=None):
+        self.begin_path("feed")
+        self.add_arc(x, y, z, i, j, k, r, 1)
+        self.end_path()
+        
+    def tool_change(self, id):
+        self.file_out.write('\t\t<tool')
+        if (id != None) : 
+            self.file_out.write(' number="'+str(id)+'"')
+            self.file_out.write(' />\n')
+        self.t = id
+            
+    def current_tool(self):
+        return self.t
+            
+    def spindle(self, s, clockwise):
+        pass
+    
+    def feedrate(self, f):
+        pass
+
+    def add_line(self, x, y, z, a = None, b = None, c = None):
+        self.file_out.write('\t\t\t<line')
+        if (x != None) :
+            self.file_out.write(' x="%.6f"' % x)
+        if (y != None) :
+            self.file_out.write(' y="%.6f"' % y)
+        if (z != None) :
+            self.file_out.write(' z="%.6f"' % z)
+        if (a != None) : self.file_out.write(' a="%.6f"' % a)
+        if (b != None) : self.file_out.write(' b="%.6f"' % b)
+        if (c != None) : self.file_out.write(' c="%.6f"' % c)
+        self.file_out.write(' />\n')
+        if x != None: self.oldx = x
+        if y != None: self.oldy = y
+        if z != None: self.oldz = z
+        
+    def add_arc(self, x, y, z, i, j, k, r = None, d = None):
+        self.file_out.write('\t\t\t<arc')
+        if (x != None) :
+            self.file_out.write(' x="%.6f"' % x)
+        if (y != None) :
+            self.file_out.write(' y="%.6f"' % y)
+        if (z != None) :
+            self.file_out.write(' z="%.6f"' % z)
+        if (i != None):
+            if self.oldx == None: print 'arc move "i" without x set!'
+            else: self.file_out.write(' i="%.6f"' % (i - self.oldx))
+        if (j != None):
+            if self.oldy == None: print 'arc move "j" without y set!'
+            else: self.file_out.write(' j="%.6f"' % (j - self.oldy))
+        if (k != None):
+            if self.oldz == None: print 'arc move "k" without z set!'
+            else: self.file_out.write(' k="%.6f"' % (k - self.oldz))
+        if (r != None) : self.file_out.write(' r="%.6f"' % r)
+        if (d != None) : self.file_out.write(' d="%i"' % d)
+        self.file_out.write(' />\n')
+        if x != None: self.oldx = x
+        if y != None: self.oldy = y
+        if z != None: self.oldz = z