Instead of explicitly calling "notifyDataSetChanged" after setting
values on a ParticipantDisplayItem now the adapter observes all its
items and calls "notifyDataSetChanged" automatically when any of them
changes.
Although this adds some boilerplate code it will make possible to update
the ParticipantDisplayItems and automatically propagate the changes to
the adapter when a model changes, rather than having to explicitly do it
from the CallActivity.
Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>
