Release Candidate Firmware V1.21 RC4

[ianski]

RC3:
- changed the order for modular track player so tables are handled right after the FX
- Mark, Copy + Paste + Delete now possible in the sequencer screen while a running sequencer
- Even more CV16 stuff under the hood

I haven't updated to 1.21, will do over the weekend but it sounds like some very cool features added indeed yet again. Adding oscillators is genius and makes the Nerdseq even more versatile.

I'm particularly happy about being able to edit/delete while running, that is going to be great for performance and also helps to keep the flow going being able to do edits on the fly.

Looking forward to the CV16 expander, will be sure to pick one up when it's available. Wonderful work!