Replaces the list of points in TempoMap with TempoSection functions, which
compute tempo-at or tick-at time relative to tempo section start.
TempoMap consults them additively to determine things like bbt_time(),
frame_time() get_grid() etc.
This has a marked effect on scrolling speed along with the code simplification
in the places it has been attempted.
Several things are broken here.
Currently every ramp except the last one is an exponential ramp. this may
be simple to fix :).
Mouse-over midi grid doesn't match mouse click grid. should also be simple.
Many things seem to work, but their accuracy should be in question until
each area has been addressed.
opening a recent session from a session can result in: Editor::constructed
and session_loaded() being true. A partial instant_save can occur (not
to mention: invalid XMLnode iterators)
This functor/closure is responsible for stealing focus from any existing text entry (or whatever else may have focus)
when clicking on a CairoWidget or derived class.
The old implementation just gave focus back to the editor canvas. The new version walks up the widget packing
heirarchy to find a focusable parent (from the CairoWidget for which it is invoked). If no focusable parent
is found, it cancels keyboard focus in the toplevel window containing the CairoWidget
I would have loved to split this apart, but there are just so many interrelated changes,
it makes little sense and would be a huge effort that would break future git bisect
use because so many intermediate commits would not compile
'Cut time' implies that the cut timeline items might end up on the
clipboard to be pasted somewhere: this isn't the case at present, so rename
the functions, class, &c. to say 'remove' rather than 'cut'.
Rename insert_time_dialog.{cc|h} to insert_remove_time_dialog while we're
at it.
Add options to move glued & locked markers to Editor::cut_time(), in line
with the insert_time() implementation.
Fix up the order in which operations apply to range marker start & end
points, to avoid problems when a range which lies after the cut point is
shorter than the length of the cut.
