Analogue-sequencer

And before anyone asks, the 'playlist step' label alongside 
the 'part' numbers is for the imminent changes to playlist edit to 
(hopefully) make it a bit more straightforward.

I've also succesfully tested a 24 MHz crystal with the new CPU, and 
will be adding support for old and new speeds to future builds.
24 MHz will be the standard clock speed for AT89C51ED2 based P3s.
I'll update the BoM shortly.

Cheers,
Colin f