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/Sketcher/Gui/Workbench.cpp

@@ -136,12 +136,16 @@ inline void SketcherAddWorkspaceArcs<Gui::MenuItem>(Gui::MenuItem& geom){
     geom    << "Sketcher_CreateArc"
             << "Sketcher_Create3PointArc"
             << "Sketcher_CreateCircle"
-            << "Sketcher_Create3PointCircle";
+            << "Sketcher_Create3PointCircle"
+            << "Sketcher_CreateEllipse"
+            << "Sketcher_CreateArcOfEllipse";
 }
 template <>
 inline void SketcherAddWorkspaceArcs<Gui::ToolBarItem>(Gui::ToolBarItem& geom){
     geom    << "Sketcher_CompCreateArc"
-            << "Sketcher_CompCreateCircle";
+            << "Sketcher_CompCreateCircle"
+            << "Sketcher_CreateEllipse"
+            << "Sketcher_CreateArcOfEllipse";
 }
 template <typename T>
 void SketcherAddWorkspaceRegularPolygon(T& geom);
@@ -177,9 +181,32 @@ inline void SketcherAddWorkbenchGeometries(T& geom){
             /*<< "Sketcher_CreateDraftLine"*/;
 }
 
-
 template <typename T>
-inline void SketcherAddWorkbenchConstraints(T& cons){
+inline void SketcherAddWorkbenchConstraints(T& cons);
+
+template <>
+inline void SketcherAddWorkbenchConstraints<Gui::MenuItem>(Gui::MenuItem& cons){
+    cons    << "Sketcher_ConstrainCoincident"
+            << "Sketcher_ConstrainPointOnObject"
+            << "Sketcher_ConstrainVertical"
+            << "Sketcher_ConstrainHorizontal"
+            << "Sketcher_ConstrainParallel"
+            << "Sketcher_ConstrainPerpendicular"
+            << "Sketcher_ConstrainTangent"
+            << "Sketcher_ConstrainEqual"
+            << "Sketcher_ConstrainSymmetric"
+            << "Separator"
+            << "Sketcher_ConstrainLock"
+            << "Sketcher_ConstrainDistanceX"
+            << "Sketcher_ConstrainDistanceY"
+            << "Sketcher_ConstrainDistance"
+            << "Sketcher_ConstrainRadius"
+            << "Sketcher_ConstrainAngle"
+            << "Sketcher_ConstrainInternalAlignment";
+}
+
+template <>
+inline void SketcherAddWorkbenchConstraints<Gui::ToolBarItem>(Gui::ToolBarItem& cons){
     cons    << "Sketcher_ConstrainCoincident"
             << "Sketcher_ConstrainPointOnObject"
             << "Sketcher_ConstrainVertical"
@@ -196,7 +223,6 @@ inline void SketcherAddWorkbenchConstraints(T& cons){
             << "Sketcher_ConstrainDistance"
             << "Sketcher_ConstrainRadius"
             << "Sketcher_ConstrainAngle";
-
 }
 
 template <typename T>
@@ -212,13 +238,15 @@ inline void SketcherAddWorkbenchTools<Gui::MenuItem>(Gui::MenuItem& consaccel){
 		<< "Sketcher_SelectHorizontalAxis"
         << "Sketcher_SelectRedundantConstraints"
         << "Sketcher_SelectConflictingConstraints"
-        << "Sketcher_SelectElementsAssociatedWithConstraints";
+        << "Sketcher_SelectElementsAssociatedWithConstraints"
+        << "Sketcher_RestoreInternalAlignmentGeometry";
 }
 template <>
 inline void SketcherAddWorkbenchTools<Gui::ToolBarItem>(Gui::ToolBarItem& consaccel){
     consaccel << "Sketcher_CloseShape"
         << "Sketcher_ConnectLines"
-        << "Sketcher_SelectConstraints";
+        << "Sketcher_SelectConstraints"
+        << "Sketcher_RestoreInternalAlignmentGeometry";
 }
 
 template <typename T>