Zones overhaul updates

[joshuavictorchen]

Description

Merge the working zones-related branches into one.

1. Update reactors module such that a Core is given an empty Zones upon instantiation (instead of None)
2. Remove references to zoning strategy hooks and reactors.buildZones: zones will be implemented in downstream applications via Interfaces
3. Move buildManualZones function to the Core class (if called, then Core.zones is set up using the zoneDefinitions case setting

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any bug fixes or new features.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[CLAassistant]

All committers have signed the CLA.

[joshuavictorchen]

Added unit tests to clear the coverage checks, which led me to discover and fix a bug with Zones.getAllLocations. Hopefully we get the green checks, now :)