[FEM] Elmer: add support for 3D magnetodynamics

- adds the corresponding Elmer equation (it is now possible to do Elmer's tutorial example no. 14)

src/Mod/Fem/femsolver/equationbase.py

@@ -129,6 +129,16 @@ class HeatViewProxy(BaseViewProxy):
         return ":/icons/FEM_EquationHeat.svg"
 
 
+class MagnetodynamicProxy(BaseProxy):
+    pass
+
+
+class MagnetodynamicViewProxy(BaseViewProxy):
+
+    def getIcon(self):
+        return ":/icons/FEM_EquationMagnetodynamic.svg"
+
+
 class Magnetodynamic2DProxy(BaseProxy):
     pass