WIP: Pitch automation improvements in Piano Roll

**Do not merge *just* yet**
*Feel free to contribute to this branch*

I've started making some usability improvements to the detuning feature in the piano roll.
(Reopened as a pull request, as it makes more sense that way)

A list of goals:
- [x] First point doesn't have to be 0
- [x] Correct scale
- [x] Draw lines instead of just points:
- [x] *Discrete*
- [x] *Linear*
- [ ] *Spline*
- [ ] Don't display the initial point if there is no automation

Optionally:
- [ ] Edit automation directly in the piano roll