Dark theme: add all lexers and the matplotlib toolbar

[tmichela]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 80.30303% with 13 lines in your changes missing coverage. Please review.

Project coverage is 75.95%. Comparing base (a0b022f) to head (5194339).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
damnit/gui/plot.py	62.85%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #378      +/-   ##
==========================================
- Coverage   75.99%   75.95%   -0.04%     
==========================================
  Files          33       33              
  Lines        5473     5490      +17     
==========================================
+ Hits         4159     4170      +11     
- Misses       1314     1320       +6     

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[tmichela]

I'll merge later today, unless someone shoots.