Improvement of rotations

Rotation:
-	Add a private attribute Vector to store the direction of the rotation, and manage not to erase this direction when the angle id 0.
-	Add a private attribute to store the angle as defined (no modulo etc)
-	Keep the quaternion for calculations

PropertyGeo
-	Saves the rotation with angle and direction instead of saving the quaternion.
-	Attribute name chosen: Ox, Oy and Oz for the coordinates of the axis and A for the angle in radians. This has to be validated.
-	Backward compatibility with the saved files with quaternion (test presence of A to determine which of  the Quaternion (old way) or the direction and angle is stored (new way). New files can be opened by old FreeCAD and vice-versa.

The only side effect I can imagine is that it was possible to set a vector to 0, 0, 0 if the angle was not 0, what is somehow non sense. Now when setting to 0, 0 0 the last not null vector is kept. The vector can not be null any longer.

src/Base/Rotation.h

@@ -103,9 +103,12 @@ public:
     static Rotation makeRotationByAxes(Vector3d xdir, Vector3d ydir, Vector3d zdir, const char* priorityOrder = "ZXY");
 
 
+void evaluateVector ();
 private:
     void normalize();
     double quat[4];
+	Vector3d _axis; // the axis kept not to lose direction when angle is 0
+	double _angle; // this angle to keep the angle chozen by the user
 };
 
 }