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: I18448773c64a6a0d65e7c39d008de2b371f4d556