feature_extraction: change block_stride for whitening, high pass from 1s to 0.25s, allow for a minimum downsampling rate to improve latency at expensive of computational cost

gstlal_feature_monitor: reduce number of missing channels messages, remove close connection line causing crashes upon shutdown

this enables to do multi-detector trigger generator & coincidence analysis
by inputs of channel-name, data, template, and PSDs from multiple IFOs.
In short, this is lalapps_StringSearch + ligolw_add + lalapps_burca of old pipeline.

like the old burca

__lt__() and friends

Add explicit synchronization point.

See merge request lscsoft/gstlal!10