* ref(contact-list): remove invite functionality

Removing becuase there is already a toolbar button dedicated
to opening the invite dialog. Now the contact list focuses
on showing current participants.

* squash: remove unused strings and styling

* squash: add plural to panel title

Prepare for React 16.

Instead of going through the Avatar object, call the getAvatarURL
directly so that the code flows consistently use the participant
representation within redux.

- 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.