[FEM] add icon for the new supported MYSTRAN solver

src/Mod/Fem/femsolver/mystran/solver.py

@@ -89,7 +89,8 @@ class Proxy(solverbase.Proxy):
 
 
 class ViewProxy(solverbase.ViewProxy):
-    pass
 
+    def getIcon(self):
+        return ":/icons/FEM_SolverMystran.svg"
 
 ##  @}