Fix recording MIDI

Fix recording MIDI

- Fix API call to add region(midi_region) -- set count to "1"
- Forward DataRecorded() signal
- remove botched merge/rebase"
  a4a87f56 accidentally brought back code from old-destructive API
  which was removed in af103cf3 and 08c13007
  There is no per track NonLayered record mode anymore, it's session global.
- set can_record correctly to not accidentally clear last capture sources
  for cont'd recording (toggle track's rec-arm)