added cmor code from pyremo

[larsbuntemeyer]

adds cmor code from pyremo.cmor and adatps it for use with cosmo by letting the user pass a mapping_table keyword argument, see #26. features include:

• unit checks and conversion to table unit if necessary
• automatic table fetching
• resampling to table frequencies if required.
• adding missing coordinate definitions (e.g., time bounds, vertices, etc..)
• checks against archive specifications.

• add code from pyremo
• add mapping_table keyword
• add tests

[codecov-commenter]

Codecov Report

Merging #68 (670f4c3) into master (6e380ba) will decrease coverage by 12.79%.
The diff coverage is 25.10%.

@@             Coverage Diff             @@
##           master      #68       +/-   ##
===========================================
- Coverage   79.03%   66.23%   -12.80%     
===========================================
  Files          19       20        +1     
  Lines         763     1001      +238     
===========================================
+ Hits          603      663       +60     
- Misses        160      338      +178     

Flag	Coverage Δ
unittests	66.23% <25.10%> (-12.80%)	⬇️

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

Impacted Files	Coverage Δ
cordex/cmor/cmor.py	21.67% <21.67%> (ø)
cordex/cmor/utils.py	72.72% <42.85%> (-18.02%)	⬇️
cordex/cmor/__init__.py	100.00% <100.00%> (ø)