Rename ek80 quadrant dimemsions and coordinates to beam

[emiliom]

Addresses the first, easy part of #520:

For EK80 there is already a dimension called quadrant that is conceptually equivalent (for our purposes) to the beam dimension as defined in SONAR-netCDF4 v1. We will need to rename it to beam.

This PR involved just simple search-and-replace steps.

[codecov-commenter]

Codecov Report

Merging #619 (6df4e20) into dev (70799ec) will decrease coverage by 6.67%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev     #619      +/-   ##
==========================================
- Coverage   78.75%   72.07%   -6.68%     
==========================================
  Files          40       27      -13     
  Lines        3615     3223     -392     
==========================================
- Hits         2847     2323     -524     
- Misses        768      900     +132     

Flag	Coverage Δ
unittests	72.07% <100.00%> (-6.68%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
echopype/convert/set_groups_ek80.py	96.10% <ø> (ø)
echopype/calibrate/calibrate_ek.py	80.14% <100.00%> (-13.36%)	⬇️
echopype/echodata/echodata.py	67.10% <100.00%> (-20.18%)	⬇️
echopype/echodata/__init__.py	0.00% <0.00%> (-100.00%)	⬇️
echopype/calibrate/__init__.py	0.00% <0.00%> (-100.00%)	⬇️
echopype/echodata/convention/__init__.py	0.00% <0.00%> (-100.00%)	⬇️
echopype/echodata/convention/conv.py	11.11% <0.00%> (-88.89%)	⬇️
echopype/echodata/api.py	16.66% <0.00%> (-66.67%)	⬇️
echopype/calibrate/calibrate_base.py	53.76% <0.00%> (-33.34%)	⬇️
echopype/calibrate/calibrate_azfp.py	70.21% <0.00%> (-25.54%)	⬇️
... and 19 more

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[b-reyes]

@emiliom I don't see any issue with your proposed changes. I think you can go ahead and merge this.

[emiliom]

Thanks @b-reyes ! I'll merge.