Separate CAEN serializers for BIFROST

• Replaces the clock-ticks based timeout timer with a standard library high resolution clock based timer for portability. This new timer has (nearly) the same interface as the x86-specific timer, so that the two can be switched easily for portability or performance, as needed.
• Removes the second CAEN serializer that produced pulse-heigh-spectra events for LOKI -- this same information is accessible via the AR51 producer/serializer by directly handling the raw data; and the removal has been an open issue for more than a year #607
• Replaces the first CAEN serializer by a vector of serializers that will contain one element for all instruments other than BIFROST. The BifrostGeometry specifies a per (arc, triplet)-pair serializer instead.