Schedule more and better

[ErikNatanael]

• Musical time scheduling
• Time maps
• More robust sample time scheduling
• More robust relative time scheduling incl. drift compensation
• Start node with sample accurate timing
• Schedule custom messages to nodes

Inspiration:

• https://billydm.github.io/blog/time-keeping/
• https://ardour.org/timing.html

[ErikNatanael]

Partially implemented by #12. Closing in favour of a new issue #14.