Draw subtitles timecodes in the waveform

Issue : #18 Change In time;

Draw zones in the waveform that correspond to subtitles timecodes.
The Orange colored zone is the "active subtitle".

Add or modify some timecode managment :
- F1 or Ctrl+leftClick : move current subtitle start time
  (move the previous sub end time if needed)
- F2 or Ctrl+rightClick : move current subtitle end time
  (move the next sub start time if needed)
- F3 : move current subtitle end time +
  add new subtitle entry or move the next subtitle start time
- Shift + F1 or Shift+leftClick : shift subtitle to the current position
  (move start time and end time of the current sub)
- F4 : Add new subtitle entry after current subtitle
- F5 : Delete current subtitle (workaround for issue #19 ...
  ... problem with "Delete" key, it is handled by text edit zone)

Signed-off-by: juiice <decaen.julien@gmail.com>