Fix crash when splitting regions in internal edit mode.
Use symbol for paste operation like everywhere else.
Make ControlList::paste const-correct.
Make selected control points bright red rather than vice-versa.
Use an enum for RoundMode instead of magic numbers.

No functional changes in this one (for easier auditing), but towards having
round up/down only if necessary modes, rather than kludging around that
situation with a double round as we do currently.
Add "maybe" rounding modes for rounding only if necessary.
Don't add origin value to MIDI controller regions on initial insert.

This should probably hijack the same modifier as the guard points and work the
same on all automation tracks, but I did it this way to not change behaviour of
track automation where a default is much more reasonable.
Reset repeated paste state on cut/copy.
Don't add spurious points when copy/pasting automation.
Support cut/copy/paste of several regions and lines at once.

The idea here is to do the reasonable thing, and copy objects of some
type (e.g. MIDI region, gain line) to tracks with a matching type.  The user
can override this with a track selection, which will be used straight-up.

Lost: ability to copy/paste lines across types, e.g. gain to pan.  This is
often questionable, but sometimes useful, so we will need to implement some
sort of "greedy mode" to make it possible.  Implementation simple, but not sure
what to do.  Perhaps this should only be possible if one automation track is
explicitly (i.e. via track selection) involved, and the types are at least
compatible-ish?
Support cut/copy/paste of MIDI notes and controllers at the same time.
Don't hide selected control points.

There was already code for this, but actually setting the corresponding
visibility flags seems to have been lost at some point.
Fix visibility of MIDI controller automation tracks across saves.

Fix some inaccurate/misleading comments that led to said bug.

Gracefully handle the "impossible" case where we can't figure out a state ID
for an automation track, instead of crashing.