Consolidate style and naming of highlight state

Rename some things to be consistent about how we treat highlight
states.

- Use blue highlights for focus no matter whether active highlights
  are on or off.
- Use `setFocused` instead of `setActive` when setting the focus.
- Rather than `setViewerFocus` and `setFocusedHighlights` have
  symmetrical RPC calls named 'focusAnnotations` in both directions.
- Get rid of the multiple highlight levels for focus. When showing the
  focus it's not important to darken inner highlights. The highlights
  visible mode still has multiple levels, all yellow.
- Remove the "annotator-hl-temporary" styles since we never call
  `setTemporary` anymore.
- Remove the "finalizeHighlights" event because nothing listens for it.
- Rename the scope method `isFocused` to `hasFocus` because I have a
  general preference against participial adjectives. It is much easier
  to remember always to use the basic verb or noun meaning of focus,
  with no ending. `hasFocus`, `focusAnnotations`, etc.

Removing dead code from our annotator branch and dropping the '-ed'
suffix from class names is left out for simplicity of managing a single
PR against one repo for the moment, but may be advisable.