This makes the osmNote work a bit more like other osm objects in iD.

- When working with the osm objects, we'll treat them as immutable.
  So all modifications will be through the update method:

  e.g. can do this in a repl, like chrome devtools console:
  >  n = iD.osmNote()
  osmNote { id: -1 }
  > n = n.update({ foo: 'bar' });
  osmNote { foo: "bar", id: -1, v: 1 }

- none of the other osm objects have getters, and in JavaScript all the
  properties are public anyway

This seems like a lot but the main things here are:
- remove the _loadingTiles "global" variable.  It was causing problems because
it was being checked from the callbacks, which are async.
- cleanup the caches
- use DOM API getElementsByTagName('id') to get note id
- set a lower tilezoom z13 for notes (meaning: fetch larger bounding boxes)

- open notes are red (default)
- resolved notes are green
- orange on hover
- yellow on select (also added centerEase to note location)

re: #5107 (comment)

re: 229484a#commitcomment-29560519

This sets `pointer-events: none` for the `.note-shadow` class,
to fix an amusing bug where hovering over the filled part of the comment
icon would work ok but hovering over the "dots" would not.

This commit also fixes a linter error, and switches some
lodash _forEach to normal for loops.

- don't insert multiple times into the rtree in `services/osm.js`
- use `d.id` instead of `d.key` as the key in `svg/notes.js`

uiNoteEditor was getting big!

Eagerly load user details after loading notes
(re: openstreetmap/openstreetmap-website#1921)

Also bump note tile zoom to z12. There just aren't that many notes,
so this reduces API calls.

- I made the buttons work like GitHub comment-on-issue buttons
before typing:  "Close Note" / "Comment" (disabled)
after typing:   "Close and Comment" / "Comment" (enabled)

- I removed a bunch of the event dispatches.  These are useful for sending
events to listeners/observers outside of the module.  In this case I think
we can handle most of the things from within the uiNoteEditor.  We can still
dispatch an 'update' event so that modeSelectNote can reselect and redraw
the note after some change happens to it.

TODO - make the buttons work / check the OSM API stuff.

`postNoteUpdate` can hangle status changes and comment additions
(I named it that to be like `putChangeset`)

Also renamed `user` to `loadUser` to be consistent with other calls

This call really does need for a result to be passed to the callback

This eliminates a lot of the copy-paste code in every callback.

Before: We drew 2 fontawesome comment icons, on on top of the other
After: Moved icon into iD spritesheet and gave it an actual `stroke` property that can be styled