Pylbo: better handling of balance equations

[n-claes]

PR description

This PR improves the way Pylbo handles the equilibrium balance equations. The derivatives of thermal conductions are added to the datfile in a backwards compatible way to make sure the energy balance is calculated correctly.
Plotting the balance is now interactive, similar to how the background is treated using a clickable legend.
The legend entries for the background plot are now properly latexified as well.

New features

Legolas

• Derivatives of thermal conduction are added to the datfile
• New method pylbo.get_equilibrium_balance(ds), which returns a dict containing the equilibrium balance equations

Pylbo

• Equilibrium balance plot is now interactive

[codecov]

Codecov Report

Merging #142 (f93d827) into develop (8f67a2a) will increase coverage by 0.10%.
The diff coverage is 100.00%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #142      +/-   ##
===========================================
+ Coverage    90.68%   90.79%   +0.10%     
===========================================
  Files          158      159       +1     
  Lines         8977     9048      +71     
===========================================
+ Hits          8141     8215      +74     
+ Misses         836      833       -3     

Flag	Coverage Δ
legolas	93.11% <100.00%> (+<0.01%)	⬆️
pylbo	86.70% <100.00%> (+0.36%)	⬆️

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