The inline classes for the toolbars were re-arranged
to fix non-rounded corners in the always-on-top window's
toolbar. However, those classes were also used by the
torture tests as a way to find stable elements that will
not get blown away by a react re-render. So re-wrap the
buttons with a div that will not get blown away,
add back the inline classes to those divs, and change
the CSS to round the corners in the always-on-top
window's toolbar.

Rounded corners on the first and last buttons. Size of the hangup button
on hover.

Prepare for React 16.

- Remove references to the model ContactList.
- Replace ContactListView with an empty element for attaching
  the React Component ContactListPanel, which has the same
  features as the old ContactListView.
- Create new selector for getting non-fake participants for
  ContactListPanel's props.
- Create a ParticipantCounter component to place in the contact
  list button. Previously ContactListView updated that but now
  it's a react component hooked into the participant state.
- Remove pub/sub that was used only by ContactListView.