Refactor colormap creation

[gerritholl]

Refactor colormap creation. Move functionality to trollimage where appropriate, and in particular where it's duplicated.

Bump trollimage version to 1.20 due to the requirement of pytroll/trollimage#117.

• Closes Unify colormap creations #2308
• Tests added
• Fully documented

[mraspaud]

Since this depends on new features in trollimage, I think we should set the min version of trollimage in setup.py accordingly, right?

[gerritholl]

Since this depends on new features in trollimage, I think we should set the min version of trollimage in setup.py accordingly, right?

Changed trollimage version to 1.20 in 24db9d3.

[codecov]

Codecov Report

Merging #2313 (1a0392b) into main (f7e056d) will increase coverage by 0.22%.
The diff coverage is 90.00%.

@@            Coverage Diff             @@
##             main    #2313      +/-   ##
==========================================
+ Coverage   94.36%   94.59%   +0.22%     
==========================================
  Files         310      314       +4     
  Lines       46641    47484     +843     
==========================================
+ Hits        44014    44916     +902     
+ Misses       2627     2568      -59     

Flag	Coverage Δ
behaviourtests	4.50% <20.00%> (-0.09%)	⬇️
unittests	95.21% <90.00%> (+0.20%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
satpy/enhancements/__init__.py	98.96% <85.71%> (-0.19%)	⬇️
satpy/composites/__init__.py	90.45% <100.00%> (+0.20%)	⬆️
satpy/composites/ahi.py	0.00% <0.00%> (-100.00%)	⬇️
satpy/readers/ahi_hsd.py	97.50% <0.00%> (-0.36%)	⬇️
satpy/utils.py	24.92% <0.00%> (-0.15%)	⬇️
satpy/readers/utils.py	91.95% <0.00%> (ø)
satpy/readers/eum_base.py	89.79% <0.00%> (ø)
satpy/readers/hrit_base.py	86.23% <0.00%> (ø)
satpy/composites/spectral.py	100.00% <0.00%> (ø)
satpy/readers/ahi_l1b_gridded_bin.py	100.00% <0.00%> (ø)
... and 15 more

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[coveralls]

Coverage: 95.172% (+0.2%) from 94.957% when pulling 1a0392b on gerritholl:refactor-colormap into f7e056d on pytroll:main.

[gerritholl]

codecov would seem to be confused, but considering I removed tested code, it's plausible that the total code coverage goes down

[mraspaud]

Just waiting on a conda-forge release before we merge this