promoting a highlight to an annotation doesn't indicate changed status

### Steps to reproduce
1. Create a highlight.
2. Promote the highlight to annotation by adding text and/or tags

### Expected behaviour
The "this is a highlight" icon should disappear.

### Actual behaviour
It doesn't.

### Additional details

http://jonudell.net/h/highlight-anomalies.mp4

The screencast begins with another observation: The creation of a highlight doesn't pop the sidebar. I guess this is intended, but just flagging it to verify.

The main point of the screencast is to illustrate the meat of this issue: Promoting a highlight to an annotation doesn't remove the "This is a highlight" indicator.

Reproduce the issue by creating a highlight and then promoting it to an annotation with text or tags. Start by tracing the UI state behind the "this is a highlight" icon; done means the icon disappears after promotion, while the separate sidebar observation remains out of scope.

Written by the indexing model from the issue text.