* Rename local variable `highlight` to `newlyCreatedByHighlightButton` and add
  a docstring - clarify what this piece of state actually means.

* Fix `vm.isHighlight()`: It now returns `false` for new annotations that the
  user hasn't entered any text or tags for yet (instead of `true`).

* Move the code for saving new highlights to the server into a
  `saveNewHighlight()` function that's called on AnnotationController
  instantiation instead of having it in a `$watch()` function that's called
  every time the local variable `model` changes.

  Also use the presence of `model.id` to avoid re-saving highlights that have
  already been saved - instead of abusing the `highlight`
  (now `newlyCreatedByHighlightButton`) variable and confusing what it
  represents.

* Don't automatically open the annotation editor on Annotationcontroller
  instantiation if the annotation is a highlight. This fixes this bug:

  1. Create a new highlight while logged out
  2. Log in
  3. Your highlight is saved to the server, but also the annotation editor is
     open on your highlight.

  The intention is that highlights are simply saved to the server, not opened
  for editing.

  _Annotations_ created while logged out, on the other hand, are _not_ saved
  to the server on login but _are_ opened for editing on login.

Refactor annotation controller tests

Remove gloval `controller` variable from AnnotationController tests.

Move the tests for annotation.js's top-level function out of the
'AnnotationController' describe() - these functions aren't part of
AnnotationController and their tests don't need all the setup in this
describe().

Wrap the annotation directive tests in a new top-level describe that's
for the entire file annotation.js, not just AnnotationController or the
annotation directive.

Refactor annotation controller, part 1

Move scope.feature() from the annotation directive to vm.feature() in
the AnnotationController. Just trying to move as much as possible out of
the directive's scope and link function into the controller, if we're
gonna use a directive controller here try to just use it instead of
randomly using the link function and scope for some things and the
controller for others.

It doesn't appear to be possible for model to be null.

Move the DOM event listener function that saves an annotation on
Ctrl+Enter into AnnotationController. This is just for the sake of
keeping all the code in one place (in AnnotationController, not in the
directive's link function) and putting code where it can be tested more
easily.

Note that the controller's save() function was previously called with
scope.$evalAsync() and we're now just calling it synchronously. This
seems to be fine.

Remove AnnotationController's vm.preview as it doesn't appear to be
used.

Replace AnnotationController's vm.editing boolean with a vm.editing()
method.

This removes some duplicated state, as both vm.editing and vm.action
were recording whether or not the annotation was being edited.

Move scope.share() from the annotation directive to vm.share() in
the AnnotationController. Just trying to move as much as possible out of
the directive's scope and link function into the controller, if we're
gonna use a directive controller here try to just use it instead of
randomly using the link function and scope for some things and the
controller for others.

It does not change after directive linking, there's no reason to
$observe() it.

Translate annotation.coffee to JavaScript

Fixes a bug that crept in during the annotation.coffee -> annotation.js
translation.

Declare variables on the same line where they're first defined, instead
of at the top of the function.