Navigation toolbar coexistence event framework

With this MEP we are planning on touching all the backends, but slowly, starting with these two. 
Hopefully, we will touch the other backends when the bigger changes are implemented, so we have to touch them only once. 
Is not the right/wrong way to do it, it is that the right way now, might be the wrong way latter. So it is preferable not touching big Base classes, unless strictly necessary for the moment.