Use lal.GPSTimeNow to get current time instead of lalapps_tconvert

See merge request lscsoft/gstlal!9

instead of calling out to lalapps_tconvert

Makefile.gstlal_feature_extractor_offline: fix issue with generating segments from int8s conversion, add default safety info, clean up comments and unused variables

gstlal_feature_extractor_pipe: link feature combiner job to run after all feature extraction jobs are finished

gstlal_feature_extractor_pipe: fix some issues with changed imports, update params in offline makefile

- there was a time when streamthinca needed to define a special class to be
  used for triggers to allow the coincidence algorithm to work, and so it
  made sense for the definition to live in streamthinca where the
  requirements were defined.  today no special class is required, the
  underlying trigger class is simply used as-is, but code like lloidhandler
  is still importing the symbol from streamthinca instead of importing it
  themselves directly.  this patch untangles this now gratuituous
  interdependency.