Sketcher New Feature: Ellipse support

- Ellipse introduction button via (center,majaxis extreme, a point in edge), ellipse is always CCW so that Z axis goes in the positive direction of the sketch
- Backwards compatibility with files of previous versions of ellipse not defining a phi angle
- Art by Jim (all the icons you see and the XPMs shown on creation of an ellipse)
- Element Widget support for ellipses
- Box selection for ellipses
- Point on Ellipse constraint based on the gardener's method based on Ulrich's function proposal (radcan simplified, i.e. with simplify_radical sage function)
- Tangent: Ellipse to Line based on DeepSOIC's geometric formulation (radcan simplified)

Sketcher New Feature: Internal Alignment Constraint
- The element to which internal alignment is applied has to be selected last.
- All other elements are added in the order of priority, taking into account existing elements
- Art by Jim (beautiful icons).

Sketcher New Feature: Tool to show/hide/restore the internal geometry of an element
- New functionality for show/hide internal geometry:
  toggles between hiding all unused internal geometry elements and showing all internal geometry.
  The restore function is implicit to the showing all internal geometry

Sketcher New Feature: Arc of Ellipse support
- Part::Geometry + Python implementation
- ArcOfEllipse creation method
- Art by Jim (all the icons you see and the XPMs shown on creation of arc of ellipse elements)
- Sketcher Element widget for ArcOfEllipse.

Bug fix: Select elements associated to constraints works now for foci internal alignment constraints

src/Mod/PartDesign/Gui/Workbench.cpp

@@ -172,6 +172,10 @@ Gui::MenuItem* Workbench::setupMenuBar() const
     Gui::MenuItem* cons = new Gui::MenuItem();
     cons->setCommand("Sketcher constraints");
     SketcherGui::addSketcherWorkbenchConstraints( *cons );
+    
+    Gui::MenuItem* consaccel = new Gui::MenuItem();
+    consaccel->setCommand("Sketcher tools");
+    SketcherGui::addSketcherWorkbenchTools(*consaccel);
 
     Gui::MenuItem* part = new Gui::MenuItem;
     root->insertItem(item, part);
@@ -233,6 +237,10 @@ Gui::ToolBarItem* Workbench::setupToolBars() const
     cons->setCommand("Sketcher constraints");
     SketcherGui::addSketcherWorkbenchConstraints( *cons );
 
+    Gui::ToolBarItem* consaccel = new Gui::ToolBarItem(root);
+    consaccel->setCommand("Sketcher tools");
+    SketcherGui::addSketcherWorkbenchTools( *consaccel );
+    
     return root;
 }