Base: new Rotation constructor - on vectors

The new constructor accepts wanted directions of x,y,z axes of rotated
frame, and a priority string that affects how the vectors are made
perpendicular to each other.

Example - construct placement for sketch on XZ plane:

v = App.Vector
App.Rotation(v(1,0,0),v(0,0,1),v())

src/Base/RotationPy.xml

@@ -25,6 +25,10 @@
 				-- three floats (Euler angles) as yaw-pitch-roll in XY'Z'' convention
 				-- four floats (Quaternion) where the quaternion is specified as:
 				   q=xi+yj+zk+w, i.e. the last parameter is the real part
+				-- three vectors that define rotated axes directions + an optional
+				   3-characher string of capital letters 'X', 'Y', 'Z' that sets the
+				   order of importance of the axes (e.g., 'ZXY' means z direction is
+				   followed strictly, x is used but corrected if necessary, y is ignored).
 			</UserDocu>
 		</Documentation>
 		<Methode Name="invert">