Wifi notifications: notify when wifi connects [2/2]

Options:
  off (default)
  a dry white toast
  a notification
  a notification with a sound
For those of us that survive on wifi islands in small college towns this is
a nice addition
The first notification will be canceled if it happens within 30 seconds of
ACTION_BOOT_COMPLETED to help prevent startup notification spamming. 5 of the
previous connections are stored and it will update the content description
accordingly if you've reconnected to one

Change-Id: Ib23c40a91464a064d1699a06d593f4b9ee4e1e8b