Add location groups

[miles-grant-ibigroup]

Checklist

• [x] Appropriate branch selected (all PRs must first be merged to dev before they can be merged to master)
• [x] Any modified or new methods or classes have helpful JSDoc and code is thoroughly commented
• [x] The description lists all applicable issues this PR seeks to resolve
• [x] The description lists any configuration setting(s) that differ from the default settings
• [x] All tests and CI builds passing

Description

This PR adds a location group editor. Blocked waiting for server-side changes that allow these changes to be exported properly.

Blocked by https://github.com/conveyal/gtfs-lib/pull/353

A future PR will handle adding stops/locations to a location group from the map.

TODO

• [x] Adding location groups to patterns
• [x] Location Group editor could look a little nicer

[miles-grant-ibigroup]

Thanks for the review Binh -- that white screen of death bug should be resolved now.

[miles-grant-ibigroup]

Unblocking this as the server end of this is merged into dev-flex.

[miles-grant-ibigroup]

@binh-dam-ibigroup the bug you reported was reproducible, but with the latest datatools-server things are working again.

Unblocking as the server-side of this is merged