Make context the first argument of operation objects
Add Paste operation to edit menu when opening the context menu on a blank area of the map (close#2508)
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
Trying to eliminate the minimum 10m distance for replacing the original
junction vertex - this is a small threshold. When _not_ replacing this
vertex, the unzorro code will wreck havok on a traffic circle.
(If there is no suitable vertex to use, it will snap to a point between
the nearest vertices, see #4146)
This allows the label collision boxes for the vertices to update
during these modes. Otherwise the labels.js `isInterestingVertex()`
function doesn't consider them interesting enough to update.
