storage: fix side effects of spAmpEnvSlow relocation
arp: cleanup -- preparing sequencer add
adding 2 track step sequencer
- press SEQx to activate the sequencer, it will wait for you to play a note to start playing.
- press SEQx again to force start.
- press RECORD while the sequencer is active to edit the sequence:
  - Highest C: add rest.
  - Highest B: add tie.
  - Highest Bb: undo last add.
  - Any other note: add to sequence.
  (the display shows the current step)