show-more-ui-prefs-from-view-window is only a mixbus thing
hide a lot of color debugging noise
Use ArdourDropdown for MIDI device selector.
Structure MIDI device selector by manufacturer.

Unfortunately we store the state of models as simply model, so if there's ever
duplicate model names, we're somewhat screwed, but this makes the (previously
unmanageably huge) menu usable, while retaining the "model name as global
identifier" state unmodified.
Fix crash if new tempo is set to start at bar #0
Fix crash if new tempo is set to start at bar #0 / Follow-up for non movable tempos
Fix crash if new tempo is set to start at bar #0 / Follow-up for non movable meters