[FEM] Elmer add support for nonlinear elasticity solver

- adds new equation "Deformation" (this name since the stress solver got in FreeCAD the misleading name "elasticity")

- this way change icon of elastic solver to make the difference clear

src/Mod/Fem/Gui/Workbench.cpp

@@ -180,6 +180,7 @@ Gui::ToolBarItem* Workbench::setupToolBars() const
         << "FEM_SolverZ88"
         << "Separator"
         << "FEM_EquationElasticity"
+        << "FEM_EquationDeformation"
         << "FEM_CompEmEquations"
         << "FEM_EquationFlow"
         << "FEM_EquationFlux"
@@ -348,6 +349,7 @@ Gui::MenuItem* Workbench::setupMenuBar() const
         << "FEM_SolverZ88"
         << "Separator"
         << "FEM_EquationElasticity"
+        << "FEM_EquationDeformation"
         << "FEM_CompEmEquations"
         << "FEM_EquationFlow"
         << "FEM_EquationFlux"