Use a beast_settings file instead of loading a sedgrid to figure our a list of filters in plot_toothpick_details

[galaxyumi]

I saw another PR by @christinawlindberg including the same changes (#710). Mine is just for the plot_toothpick_details.py, while #710 seems to include changes in other files. @karllark Please feel free to reject or accept this PR.

[codecov-commenter]

Codecov Report

Merging #715 (d99393b) into master (f5ce89d) will decrease coverage by 0.34%.
The diff coverage is 28.57%.

@@            Coverage Diff             @@
##           master     #715      +/-   ##
==========================================
- Coverage   43.73%   43.39%   -0.35%     
==========================================
  Files         100      100              
  Lines        9710     9725      +15     
==========================================
- Hits         4247     4220      -27     
- Misses       5463     5505      +42     

Impacted Files	Coverage Δ
beast/plotting/plot_toothpick_details.py	13.04% <28.57%> (ø)
beast/tools/compare_spec_type.py	60.86% <0.00%> (-33.92%)	⬇️
beast/fitting/pdf1d.py	89.83% <0.00%> (-3.20%)	⬇️
beast/fitting/fit.py	81.73% <0.00%> (-0.33%)	⬇️
beast/tools/read_beast_data.py	42.18% <0.00%> (ø)
beast/tools/run/run_fitting.py	19.11% <0.00%> (ø)
beast/observationmodel/ast/make_ast_xy_list.py	5.04% <0.00%> (ø)
beast/tools/subgridding_tools.py	32.59% <0.00%> (+0.12%)	⬆️

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[karllark]

Looks good.