Processing usage updates

[wtgee]

Misc edits during processing

• Default docker compose file to develop tag.
• Add photutils dependency in docker.
• Added an RGB IntEnum for easy iterating and consistent array access of rgb data.
• get_stamp_slice has as_slices param added with default True for legacy behavior. If False then just the four points are returned.
• get_rgb_background only accepts data as an argument.
• Updated defaults for get_rgb_background.
• Added save_rgb_bg_fits that will save a FITS files with seven extensions: combined rgb map, and then the background and rms maps for each color.
• ruamel.yaml added to base dependencies for use in serializes.

[codecov[bot]]

Codecov Report

Merging #265 (efde546) into develop (3127c4a) will increase coverage by 0.46%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #265      +/-   ##
===========================================
+ Coverage    73.13%   73.60%   +0.46%     
===========================================
  Files           31       31              
  Lines         1969     2004      +35     
===========================================
+ Hits          1440     1475      +35     
  Misses         529      529              

Impacted Files	Coverage Δ
src/panoptes/utils/images/bayer.py	100.00% <100.00%> (ø)
src/panoptes/utils/images/plot.py	21.05% <100.00%> (ø)

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