simplesim: Handle disconnects

[jajik]

When a connected configuration is loaded into the simplesim, and then it disconnects, forming two separate components, the simplesim terminates with SIGABRT if the positions of both parts are not fixed.

The simplesim should not terminate, but it should inform the user about the missing fixation. Optionally, it could fix the second part's position to that it had before the disconnect, as that is usually what the user wants (however, additional issues arise with this approach).

[Ondraceq]

I believe the second solution is something we shouldn't do - since it seems like something that the user would want, but we would strengthen the believe that nothing can happen if the user separates the rofibot in two and the tries to join them inside a reconfiguration algorithm - which should 100% be avoided.

Yes, it shouldn't abort - but this is a larger thing that should be fixed - it's not only when disconnecting.