Consolidate localization behavior and init to a coreLocalizer function and singleton
Explicitly support `en-US` locale
Rename coreData to coreFileFetcher and export a singleton rather than using a property of coreContext
Add `apiConnections` property of coreContext to simplify adding a source switcher
Replace some init functions with re-callable, promise-supporting `ensureLoaded` functions
Make coreContext itself load the UI if a container has been specified at init time
Fix code tests
Add `utilCombinedTags` method and use it for the raw tag editor as well as fields
Pass `entityIDs` array into fields instead of single `entity` object
Give field revertion its own path separate from `change`
Add multiselection editing to fields in files: access, address, check, combo, cycleway, input, maxspeed, textarea, and wikidata
Fixes issue with nested/namespaced fields, such as `maxspeed/advisory`,
in situations where would try to use a css selector or element id.
Can't use characters like '/' in a css selector.
