This adds new cursor rulers for edit, punch and playback.  P1/P2 are now known as the
Edit Cursor. Multiple Punch Cursors may be defined. The playback cursor affects Home and End
controls. New options are available for looping over the playback cursor (even while recording)
and automatically creating new takes at start of recording (or loop).

The new cursor objects bump the project file version. Older versions of non-daw will be
unable to load new/edited projects.

Fix sorting of tempomap.

Add an update_tempomap() method to Timeline instead, which must be
called every time the time or tempo tracks are edited. This is perhaps as
ugly as the unified map was, but is at least a bit more compatible with
the possibility of moving all the meat of tempomapping into a library.

Use a cross-hair cursor for control sequences.