Move click-end-node-to-finish functionality from draw modes to behaviorDraw
Fix issue where the head node would get hover-highlighted when continuing from the end of a line
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
(closes#4669)
Now instead of creating MultiLineString targets, we just create a bunch of
LineString targets. This makes the code simpler, and anyway the entity is
still there in `properties` for drawing code to decide what to do with the target.
Incidentally, this change allows iD to support an extrusion operation.
(Because each way segment has its own unique GeoJSON target now)
The goal here is that the code that draws the targets should know better
what parts of the lines/vertices are targetable, rather than just
relying on CSS to ignore the pointer events on the whole line.
e.g. when drawing a line, it's ok for it to loop back and connect
to itself, just not on a segment or vertex adjacent to the active
node.
These changes are needed now that `addNode`
* wants to preserve circularity
* automatically remove duplicates
* range checks index argument (can't call it with -1 anymore)
