Add toasts to blocked numbers.

- Add toasts on blocked/unblocked/911/duplicate.

- BlockedNumberContract.isBlocked() is a look up by number
 which is indexed so should be fast, however, to be safe
 we run in an async task. So I moved all work for adding
 blocked number to the asynctask.

Bug: 27495710
Change-Id: Ia56de55f3161c5d413a55adb37668b720f634ef3