The AudioClipEditor features a scroll bar that is a part of the canvas. Because scroll
groups are at the top level of a canvas, the scroll bar is necessary within a scroll
group, which causes it to get confused about the difference between its own
position within the canvas and that of the scroll group. This commit introduces
a per-Item flag, _scroll_translation, which is true by default. If false, the
item will not have coordinates translated to reflect scroll group position.
When importing a multi-track MIDI files with identical track-names,
Ardour would create the same file for each track. Effectively
overwriting an existing file.
The following MIDI file would create the same file twice
in `interchange/`, once for each MTrk.
```
MFile 1 2 240
MTrk
0 Meta SeqName "Foo Bar"
0 TimeSig 4/4 24 8
0 Tempo 666667
0 Meta TrkEnd
TrkEnd
MTrk
0 Meta TrkName "Foo Bar"
0 On ch=10 n=36 v=95
...
```
During drag-motion callbacks the data to be dragged is n/a.
However we like to discriminate if drop is possible.
When dragging regions, the data-type of the region to be dragged
is unknown, so different `x-ardour/region` targets are not an
option, either.
Until a better option is presented, a static global is used
to set the data-type for region.pbdid drags.
See also af69061644 and b8e1cd53c. This can be useful in
some cases where running a dry-run build will fail.
e.g. with --freedesktop files that are not generated before the
actual build.
Major changes: do not delete and recreate markers and curves for every tempo map
change, attach tempo curves directly to their (preceding) tempo marker, notable
cleanup of TempoCurve class to remove unnecessary members.
More tweaks expected since algorithm for matching markers and tempo map
points is not correct yet.
