Draw unknown substituent

[urbj]

Description of Changes

-Replaced all unknown/out of lib residues with the Unknown glyph before drawing
-Changed substituent notation from Subsituent to Subst for space reasons
-Subst stays visible even on Unknown residues
...

Changelog

• I have added my changes to CHANGELOG.md under the appropriate module/submodule section

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.52%. Comparing base (4426a5c) to head (4bbde22).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #110      +/-   ##
==========================================
- Coverage   96.53%   96.52%   -0.01%     
==========================================
  Files          18       18              
  Lines        7091     7107      +16     
==========================================
+ Hits         6845     6860      +15     
- Misses        246      247       +1     

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