* Narrow Variable editor state using selector functions
- Explicitly type "extended" editor state in editor/reducter.ts using a union
- Create selectors to narrow the types, using unique properties from each extended state to discriminate the union
- Update DataSourceVariableEditor to use new style of redux connector
- Update variable editor components to use new selectors
* fix tests
* Make adhoc variable infoText optional, because it is!
* Add AdHocVariableEditor tests
* DataSourceVariableEditor tests
* comment
* reset
* Wrote tests for selectors \(that actually caught a bug, whodathunkit)
* fix stray types and lint issues
* Rename selector functions
