Testing needs more detailed effort in the find/plot_[pipeline]_event areas

[texadactyl]

In addition to the current Github Actions CI testing and before executing a merge function at the BL main branch, we need to also have:

• assurances that filter threshold levels work as expected in find_event_pipeline
• checks on the CSV file produced by find_event_pipeline
• manual visual inspection of PNG files produced by plot_event_pipeline/plot_event

To do: add the Voyager 2020 h5 set to the test process along those lines.

[texadactyl]

As of today (2020-01-09), test/test_pipelines.py has been updated as follows:

• Use Voyager 2020 HDF5 files as input for FindDoppler.
• Specify filter_threshold=3 for find_event_pipeline().
• Validate the CSV file (selected columns) and the Pandas dataframe from find_event_pipeline().
• Ensure that exactly 6 PNG files are produced from plot_event_pipeline().