Show infinity for large notification counts

This patch adds a new string to SystemUI for displaying the infinity
symbol when a notification has a count larger than 999.  This only
affects the notification icon in the status bar and does not change
the text displayed in the actual notification.

Change-Id: Ie1b06c888a7e4e82147bb930b2715a3e97b6f009
REF: CYNGNOS-592