Add first release of graphite database

[trappitsch]

This PR does not just add the first graphite database on Zenodo, but also extends all the tooling in order to accept graphite databases in teh future!

• update bib file with graphite references
• extend reference appending capability and add graphite refs to database
• refractor and update techniques files by appending from graphite db excel
• extend db addition to graphites and add first graphite release to database
• update database with graphites and fix tests

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.37%. Comparing base (d67db3b) to head (7a5870b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #40      +/-   ##
==========================================
+ Coverage   83.36%   84.37%   +1.01%     
==========================================
  Files          11       11              
  Lines         571      608      +37     
==========================================
+ Hits          476      513      +37     
  Misses         95       95              

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[pep8speaks]

Hello @trappitsch! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file src/pgdtools/maintainer/__init__.py:

Line 9:80: E501 line too long (82 > 79 characters)

• In the file src/pgdtools/maintainer/excel_tools.py:

Line 31:80: E501 line too long (81 > 79 characters)
Line 32:80: E501 line too long (86 > 79 characters)
Line 49:80: E501 line too long (87 > 79 characters)
Line 153:80: E501 line too long (82 > 79 characters)
Line 155:80: E501 line too long (80 > 79 characters)
Line 158:80: E501 line too long (86 > 79 characters)
Line 202:80: E501 line too long (83 > 79 characters)
Line 204:80: E501 line too long (80 > 79 characters)
Line 208:80: E501 line too long (81 > 79 characters)
Line 246:80: E501 line too long (84 > 79 characters)
Line 251:80: E501 line too long (80 > 79 characters)
Line 262:80: E501 line too long (84 > 79 characters)
Line 267:80: E501 line too long (82 > 79 characters)

• In the file tests/test_maintainer/test_excel_tools.py:

Line 91:80: E501 line too long (81 > 79 characters)
Line 116:80: E501 line too long (82 > 79 characters)
Line 175:80: E501 line too long (84 > 79 characters)