add event for confirming changes in Layout Editor

[commy2]

When merged this pull request will:

• title
• close Event for confirming changes in the Layout Editor #1070

Example:

["CBA_layoutEditorSaved", {
    systemChat str [diag_tickTime, _this];
}] call CBA_fnc_addEventHandler;

Note: Add in XEH_preInit to ensure this working in the main menu and 3den. Adding the event in preInit might or might not require to put cba_events in requiredAddons of the component of the XEH preInit event.