Rename Kromer Plot to Spectral Element Decomposition (SEDec) Plot

[jaladh-singhal]

Renamed Kromer by Spectral Element Decomposition (SEDec) throughout the module and also renamed the module.

Motivation and Context

Kromer Plot name is very uninformative to the broader community. Also as @wkerzendorf pointed out:

There has been a push in general in astronomy to separate ideas from names for several reasons (e.g. renaming maxwell equations).

How Has This Been Tested?

• Testing pipeline
• Reference Data Comparison following these instructions
• Other (please describe)

I've ran the Kromer Plot demo notebook after these changes, everything works as expected.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• None of the above (please describe)

Checklist:

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have built the documentation on my fork following these instructions
• I have assigned and requested two reviewers for this pull request

[codecov]

Codecov Report

Merging #1424 (5864c3f) into master (a6d190c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1424   +/-   ##
=======================================
  Coverage   71.16%   71.16%           
=======================================
  Files          67       67           
  Lines        5521     5521           
=======================================
  Hits         3929     3929           
  Misses       1592     1592           

Impacted Files	Coverage Δ
tardis/tardis/widgets/kromer_plot.py
tardis/tardis/widgets/sedec_plot.py	16.43% <0.00%> (ø)

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[jamesgillanders]

So this all looks good, but are we definitely going with SED or is this needing to be updated/changed?

[jaladh-singhal]

Since SED already stands for Spectral Energy Distribution, changed it to SEDec