Display missed call count for call log.

The number of unread missed calls are displayed beside the Call Log as a
badge. All unread missed calls are bolded under the call log tab. When
exiting the call log tab, all unread calls are marked as read. When
interacting with an unread missed call card while in the call log tab,
it will subtract 1 from the badge.

BUG=24953555

Change-Id: If91a3bc89197465934cb773955e4bec005d6d14e