* 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

- 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.

With interfaceConfig.SHOW_CONTACTLIST_AVATARS, the avatars in the
contact list are too big and will overlap each other. Constrain
the avatar sizes and make each contact a little taller to better
space each out.