AutomationPattern::addObject now returns a boolean which indicates
whether the object was added or not. This change enables the removal of
the error message that is shown in the case that a model is already
connected from AutomationPattern::addObject. Instead all interactive
callers now check for the return value and show the message in case it
This change set improves the import of MIDI files significantly. These
have been slowed down quite a lot due to the message being shown
repeatedly during the MIDI import.