Improve MMC3 mapper, SMB3 title screen renders correctly

Add RP2C02.TriggerScanlineCounter method which is used by
NES.runProcessors to determine if MMC3's scanlineCounter method should
be called.  This is much easier and just as effective as trying to
listen to the PPU's memory bus to watch for A12 going high.

Removed memory tracing support from RP2A03.MappedMemory as it is no
longer used.  Simiarly removed NeedTraces/Trace methods from ROM
interface