fix CSW service / version support (optional in 3.0.0) (#544)

[tomkralidis]

Overview

In CSW 3, service and version parameters are optional (required in CSW 2.0.2). This PR does deeper detection of CSW 2 vs. 3 requests and handles/sets service and version accordingly.

Related Issue / Discussion

#544

Additional Information

Contributions and Licensing

(as per https://github.com/geopython/pycsw/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• I'd like to contribute [feature X|bugfix Y|docs|something else] to pycsw. I confirm that my contributions to pycsw will be compatible with the pycsw license guidelines at the time of contribution.
• I have already previously agreed to the pycsw Contributions and Licensing Guidelines

[codecov]

Codecov Report

Merging #552 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #552      +/-   ##
==========================================
+ Coverage   55.93%   55.98%   +0.05%     
==========================================
  Files          29       29              
  Lines        6338     6346       +8     
  Branches     1342     1345       +3     
==========================================
+ Hits         3545     3553       +8     
  Misses       2412     2412              
  Partials      381      381

Flag	Coverage Δ
#integrationtests	54.63% <100%> (+0.05%)	⬆️
#unittests	7.62% <0%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pycsw/server.py	65.58% <100%> (+0.57%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fe4edd7...58886dd. Read the comment docs.