Separate payload paths and queues

[charlieparkes]

Change Payload to split paths into paths and queues. Update all logic to assume only path strings / enums are in payload.paths.

[codecov]

Codecov Report

Merging #23 into master will decrease coverage by 0.25%.
The diff coverage is 94.20%.

@@            Coverage Diff             @@
##           master      #23      +/-   ##
==========================================
- Coverage   93.55%   93.29%   -0.26%     
==========================================
  Files          18       18              
  Lines         698      716      +18     
==========================================
+ Hits          653      668      +15     
- Misses         45       48       +3     

Impacted Files	Coverage Δ
lpipe/payload.py	88.00% <76.92%> (-12.00%)	⬇️
lpipe/pipeline.py	87.39% <97.87%> (+0.61%)	⬆️
lpipe/action.py	100.00% <100.00%> (ø)
lpipe/normalize.py	91.66% <100.00%> (-0.65%)	⬇️

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