Warn when exception is encountered during saving

[sandorstormen]

Multiple times now, I have tried to save my scenario. Believing it to be saved, I have then exited out of the mal-gui. This has happened because there is no feedback whether the saving worked or not. The mal-gui should give some feedback whether saving worked or not.

[mrkickling]

Yes, this is for sure a general issue. We should display errors in the GUI and not just print them in the cli.