Deduplicate React state

[patcon]

🎈 User Story: https://trello.com/c/aUD04RjO/113-story-%E2%9C%A8-as-start-staff-i-want-the-map-to-always-be-displaying-the-most-current-information-so-that-am-confident-what-i-am-seeing

Prior to this, start-map was storing state as objects (specifically geojson feature objects) in a few different react states. This changes that to:

• visFtrs => visibleFeatureIds: array of integers for feature ids
• allFeatures: no change (maintains full static array of objects for reference)
• activeFeature => activeFeatureId integer for feature id

Did some general renaming of vars and functions for consistency, to know better what args are expected for each.

This PR will make it simpler to populate and "hydrate" data from live data in next PR.

Definition of Done Checklist:

• Documented
• Deployed to staging
• No errors bugs/regressions introduced
• Added performance test results to PR
• Reviewed by Product Owner (via screencast) -- if appropriate
• Chore/task/feature merged into master

Performance Test Results

Speed test	Score: master	Score: this PR
GTMetrix	36% / 85%	XX% / XX%
PageSpeed Insights	20/100 & 33/100	/100 & /100

[patcon]

Found a bug that showing on review app, and investigating.