The previous version had various issues, in particular
when creating Tracks with an instrument, the RouteUI was not
available when the signal was emitted (likely caused by recent
ee-work of Audio+MIDI and Tape track removal).
However as side-effect fanned-out tracks/busses may now
be ordered before the new instrument route.
This also fixes an edge case of multiple fan-out in case
there is more than one RouteUI instance (mixer, editor-mixer,
meter-bridge).