Added support for username/password for sparqlwrapper

[jesper-friis]

Description

Added support for username/password for sparqlwrapper.

A CI test would require an online triplestore to test against. Therefore not added. However, the following seems to work:

from tripper import Triplestore

ts = Triplestore("sparqlwrapper", base_iri="https://graphdb.pink-project.eu/repositories/playground", username="USER", password="XXX")
print(list(ts.triples))

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 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 76.85%. Comparing base (c1e8213) to head (b105b37).

Files with missing lines	Patch %	Lines
tripper/backends/sparqlwrapper.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #308      +/-   ##
==========================================
- Coverage   76.87%   76.85%   -0.03%     
==========================================
  Files          22       22              
  Lines        2465     2467       +2     
==========================================
+ Hits         1895     1896       +1     
- Misses        570      571       +1     

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