* show _region_line dropdown and label (previously ArdourHSpacer
was packed in their place)
* add spacer at the bottom of the window to not prevent
spreading out of clocks or other elements.
Filling the CC dropdown menus of the editor's pianroll
bottom attachment can take ages.. So only do that when
the bottom pane is actually visible.
This will need more work, since it's still slow, and the
menu is also not correctly using sub-menus.
* Only show progress bar when downloading/installing
* Don't allow re-install
* Scale progress bar width with UI
* make sure target clip library folder exists
Found via `codespell -q 3 -S "*.pdf,*.po,./.git,*.tosc,./waf,./share/patchfiles,./libs,./msvc_extra_headers,./share/web_surfaces,*.patch" -L acount,addin,ane,ba,buss,busses,caf,capela,devine,disconnectin,discreet,doubleclick,envolution,filetest,fo,ghandi,homs,hsi,layed,maschine,mis,nd,ontop,pass-thru,removeable,retrn,ro,scrollin,sectionin,seh,siz,sord,sur,te,trough,ue,vie,wth`
Since we have only 1 type of snap (the grid, which is BBT based always), this
method doesn't need as much of the baggage as the equivalent Editor method
The history is cleared separately, we can remain connected to the signal. Nothing will happen to it that
we don't control, since we own the UndoHistory object
CueEditor::catch_pending_show_region() calls ::set_region
which calls CueEditor::unset(false). This reset _track.
Also PianorollWindow::set() calls set_track() before set_region(),
the latter also reset CueEditor::_track.
This fixes the Solo button in the Pianoroll window, and
probably some other things, too.
Mouse-mode is set after the the session sets CoreSelection
in the backend, and can clear valid selection.
Note: Region Selection (if any) is saved in instant.xml
and set during first_idle, which usually still happens
from `load_session_stage_two() -> flush_pending()`.
