- Remove unused 'toggleAiBotPanel' widget action
- Switch from appEvents to closure actions
- Convert widget definition to native class syntax, so that we can use `@action` decorator. (alternatively, we could have done `{ closePanel: this.hideAiBotPanel.bind(this) }` in `RenderGlimmer`
Previously we were not using using HeaderPanel for drop down, which caused
it not to properly act like a header panel.
- Not styled right
- Not hidden when other buttons clicked
Etc...
Header is sadly full of legacy so this is somewhat hacky weaving widgets.