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
This fixes one of the issues in #4351 where the radio button was not
selected. This was likely introduced during the upgrade to d3 v4, now
that enter selections do not automatically flow into update anymore.
(the fix is to add a `merge` to ensure that the `selection.each` actually
has some things to iterate over)
- Attempt fast save first, only perform conflict resolution if necessary (re: #3056)
- Block reentry of save, and dont keep focus on save button (closes#4641)
- Refactor modeSave() for code clarity (avoid shared state in closure variables)
