Schema validator

[jesper-friis]

Description

Main aim: Update the keyword definitions to conform to DCAT-AP.

Subgoals:

• provide an single source for defining keywords (from which json-ld files and documentation can be generated)
• make it easy to extend keywords for different fields or domains
• enable validation of data

This PR include many improvements:

• A single YAML source for defining keywords
• A pre-commit hook that generates the JSON-LD context and documentation from the keywords
• Support for additional keywords defined by other packages via entry points
• Validation of dicts with data documentation
• Fix pylint issues
• Updated the context to comply with DCAT-AP
• Updated tests to comply with DCAT-AP
• Improve search_iris(). Criterias can now be nested

Type of change

• Bug fix and code cleanup
• New feature
• Documentation update
• Testing

Checklist for the reviewer

This checklist should be used as a help for the reviewer.

• Is the change limited to one issue?
• Does this PR close the issue?
• Is the code easy to read and understand?
• Do all new feature have an accompanying new test?
• Has the documentation been updated as necessary?
• Is the code properly tested?

[codecov]

Codecov Report

Attention: Patch coverage is 88.00000% with 60 lines in your changes missing coverage. Please review.

Project coverage is 78.74%. Comparing base (be012ac) to head (744e3c6).
Report is 44 commits behind head on master.

Files with missing lines	Patch %	Lines
tripper/datadoc/keywords.py	84.46%	32 Missing ⚠️
tripper/datadoc/dataset.py	92.21%	13 Missing ⚠️
tripper/utils.py	84.84%	10 Missing ⚠️
tripper/datadoc/dataaccess.py	63.63%	4 Missing ⚠️
tripper/backends/sparqlwrapper.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #296      +/-   ##
==========================================
+ Coverage   77.91%   78.74%   +0.83%     
==========================================
  Files          22       24       +2     
  Lines        2522     2856     +334     
==========================================
+ Hits         1965     2249     +284     
- Misses        557      607      +50     

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