fix "other" port-group tab

Separate port-bundles for each jack client in the connection manager.

Previously, apps were only listed as separate bundles if the
ports were gathered at different times. ie one app shows up after
the other (and if no complete re-scan was triggered)

Fixes issue reported by Fons Adriaensen.
properly handle port removal in route.

bug:
 - add midi track
 - add additional midi port
 - remove additional midi port
 - press play
 -> crash

because..

ARDOUR::MidiTrack::roll's route_buffer still has 2 midi-channels. This is
because processor_max_streams was not updated (no plugins added/removed)
fill_buffers_with_input() eventually asserts when trying to get the 2nd
(nonexistant) midi port via ARDOUR::PortSet::nth_midi_port() in
 ARDOUR::PortSet::port().
fix gtk "child->parent == NULL" asserts
add a peak reset button to the editor meter

see http://tracker.ardour.org/view.php?id=5601