Refactor redux store to use Map

[gdetrez]

Refactor the redux store to use Maps instead of objects for entities (projects, experiments and scanners).

Maps are easier to loop through and easier to typecheck.

This also rename some fields in the actions and the selectors' results for consistency.

[codecov-io]

Codecov Report

Merging #366 into master will increase coverage by 0.03%. The diff coverage is 97.14%.

@@            Coverage Diff            @@
##           master    #366      +/-   ##
=========================================
+ Coverage   40.26%   40.3%   +0.03%     
=========================================
  Files         195     195              
  Lines       16716   16732      +16     
  Branches     2921    2921              
=========================================
+ Hits         6730    6743      +13     
- Misses       9571    9574       +3     
  Partials      415     415

Impacted Files	Coverage Δ
...anomatic/ui_server_data/js/src/projects/actions.js	84.84% <ø> (ø)	:arrow_up:
...a/js/src/projects/reducers/entities/experiments.js	100% <100%> (ø)	:arrow_up:
...tic/ui_server_data/js/src/projects/StateBuilder.js	97.26% <100%> (ø)	:arrow_up:
...data/js/src/projects/reducers/entities/projects.js	100% <100%> (ø)	:arrow_up:
...omatic/ui_server_data/js/src/projects/selectors.js	95.55% <92.85%> (-1.75%)	:arrow_down:
scanomatic/data_processing/phases/segmentation.py	74.09% <0%> (-0.56%)	:arrow_down:

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