Add SurveyDataSet, implement SDSSDataSet

[kbarbary]

This implements a "dataset" interface that can be fulfilled by different datasets, SDSS being one. The main interface is to create a dataset object, then call load_images(dataset, box). The specific dataset implementation determines where to find images overlapping the box, how to load files, and how to create Celeste Images from them.

• Add an abstract SurveyDataSet type, to be subtyped by actual implementations of datasets.

• Implement SDSSDataSet <: SurveyDataSet, implementing how to create Celeste Images from SDSS data on disk. Options in SDSSDataSet formerly lived in IOStrategy, which SDSSDataSet replaces.

• Move implementation of command-line script bin/infer-box.jl into package in main.jl in order to easily facilitate testing.

• Read both general configuration and dataset configuration from yaml file (formerly done in settings.jl, now done in main.jl).

[codecov[bot]]

Codecov Report

Merging #729 into master will increase coverage by 0.07%. The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master     #729      +/-   ##
==========================================
+ Coverage    81.5%   81.57%   +0.07%     
==========================================
  Files          38       39       +1     
  Lines        3937     3963      +26     
==========================================
+ Hits         3209     3233      +24     
- Misses        728      730       +2

Impacted Files	Coverage Δ
src/ParallelRun.jl	84.87% <100%> (-1.01%)	:arrow_down:
src/AccuracyBenchmark.jl	78.26% <100%> (ø)	:arrow_up:
src/GalsimBenchmark.jl	100% <100%> (ø)	:arrow_up:
src/config.jl	100% <100%> (ø)	:arrow_up:
src/dataset.jl	33.33% <33.33%> (ø)
src/SDSSIO.jl	97.15% <94.3%> (-0.89%)	:arrow_down:
src/main.jl	97.29% <97.29%> (ø)

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[jeff-regier]

Looks good!