FEM: Add Preferences option to hide materials from user defined directory

Signed-off-by: Przemo Firszt <przemo@firszt.eu>

src/Mod/Fem/Gui/DlgSettingsFemImp.cpp

@@ -48,6 +48,7 @@ void DlgSettingsFemImp::saveSettings()
     fc_ccx_binary->onSave();
     cb_use_built_in_materials->onSave();
     cb_use_mat_from_config_dir->onSave();
+    cb_use_mat_from_custom_dir->onSave();
     fc_custom_mat_dir->onSave();
 }
 
@@ -58,6 +59,7 @@ void DlgSettingsFemImp::loadSettings()
     fc_ccx_binary->onRestore();
     cb_use_built_in_materials->onRestore();
     cb_use_mat_from_config_dir->onRestore();
+    cb_use_mat_from_custom_dir->onRestore();
     fc_custom_mat_dir->onRestore();
 }