gstlal_feature_synchronizer + gstlal_ll_feature_extractor_pipe: fix issue where sample rate of incoming features was not being taken into account, expose option to online DAG generation

gstlal-calibration/tests:  Added more filtering options to plot_transfer_function.py so that it can handle whitened channels.

- gstlal_compute_strain:  numerous small bug fixes to get kappa_U calculation to work with new channels.
- tests/check_calibration:  Added plotting for GDS / CALCS transfer function.  Still needs dewhitening.
- debian/gstlal-calibration.install:  edits to make gstlal-calibration build on Debian

Update .gitlab-ci.yml: trying to build documentation with an older stretch container. editing in the web interface, because, yolo.

- use TYPICAL_HORIZON_DISTANCE constant instead of 100. for the typical
  horizon distance

- avoid evaluating float("-inf") in performance sensitive paths

- missing Dataless and Frankenstein ranking stats

- currently nonsense, redundant since addition of sum-of-SNR^2 cut.  the
  latter will be fixed, cleaned up, and made to incorporate this feature

- fix spelling error in name
- population_model_file needs to be passed as keyword argument in
  numerator's .splice() method

lal_transferfunction and lal_adaptivefirfilt:  Forgot to call gst_buffer_unmap() after gst_buffer_map().  Fixed that.

gstlal-calibration-1.2.3 release.  Includes a minor bug fix so that all needed plugins get built and packaged.

gstlal-calibration:  cmath plugin:  fixed typos in Makefile.am so that the plugin has the correct name.

Fixed a few typos in gstlal_compute_strain to get coherence_bits to be defined if f_s and src_q are not computed and to check for keys in act_line_removal dict before populating

- accidentally modified an in-use variable

gstlal-calibration tests:  Updated commands in Makefile to have correct titles in transfer function plots.