Predefined EMMO namespace with checking and label lookup

[jesper-friis]

Description

Enable checking and label lookup by default for the EMMO namespace. The following now works out of the box

>>> from tripper import EMMO
>>> EMMO.Atom
'https://w3id.org/emmo#EMMO_eb77076b_a104_42ac_a065_798b2d2809ad'

Also implemented lazy loading of the triplestore when a Namespace with checking or label lookup is created. This ensures that we still can import tripper without having rdflib installed, although EMMO.Atom will fail with a ModuleNotFoundError.

Added workaround for a design bug in pytest - without the completely unmotivated special handling of the __wrapped__ attribute pytest would always fail during its collection phase. We should consider to replace pytest with a more decent test framework...

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

All modified and coverable lines are covered by tests ✅

Project coverage is 79.30%. Comparing base (1d032c9) to head (cb73aff).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #261      +/-   ##
==========================================
+ Coverage   79.21%   79.30%   +0.09%     
==========================================
  Files          18       18              
  Lines        1727     1735       +8     
==========================================
+ Hits         1368     1376       +8     
  Misses        359      359              

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