tracelogger infrastructure needs CPU argument

1. core can report flags for which CPUs can be traced
2. frontend can tell core which CPU(s) to trace
3. frontend can display CPUs individually
4. frontend can interleave CPUs, in the order recorded by the core
5. to achieve 4, make trace logger interface take a serial number

this can be tested on the SNES core (CPU and GB can run concurrently, or more simply, CPU and SMP) since the traces are already forwarded from the core to the c# layer and then simply dropped due to having nowhere to go.

Minimal implementation skips item 4, but while we're in there, the interface should be upgraded to handle item 5.

Not an extremely challenging task.