QS: Show # of clients connected to hotspot

Since we no longer post a notification showing that the wifi hotspot
is on and the # of connected clients, we now show the # of clients
connected in the label of the hotspot QS tile.

Change-Id: I9ed37b96db9b5b4320a7260524f69733ea70d030

HotSpot: Store # of connected clients in receiver

Get the number of connected clients in onReceive and cache the value
to be used in handleUpdateState.

Change-Id: I011a13e186c1fa9976df58a4ad1603e6c0cd6bbb