Documentation: axis conversion

[jlaehne]

Description of the change

• Add chapter on axis conversion to documentation.
• Add links to tutorials on front page and in the menu.
• Make to_raman_shift alias for to_invcm_relative.
• Use orange for formulas (as color that works well in bright and dark mode).
• Detect if laser wavelength is in the metadata

Progress of the PR

• Change implemented (can be split into several points),
• Add figure for Jacobian,
• automatically read laser wavelength if in metadata,
• ready for review.

[codecov-commenter]

Codecov Report

Merging #113 (39d425a) into main (699be7d) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #113      +/-   ##
==========================================
+ Coverage   95.70%   95.76%   +0.06%     
==========================================
  Files          11       11              
  Lines         582      591       +9     
==========================================
+ Hits          557      566       +9     
  Misses         25       25              

Impacted Files	Coverage Δ
lumispy/signals/luminescence_spectrum.py	90.42% <100.00%> (+0.37%)	⬆️
lumispy/utils/axes.py	96.89% <100.00%> (+0.03%)	⬆️

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[jlaehne]

The new user-guide page can be found here: https://lumispy--113.org.readthedocs.build/en/113/user_guide/signal_axis.html