Adds a ReceiveText application that can be used in
conjunction with SendText. Currently, there is no
way in Asterisk to receive text in the dialplan
(or anywhere else, really). This allows for Asterisk
to be the recipient of text instead of just the sender.

ASTERISK-29759 #close

Change-Id: Ica2c354a42bff69f323a0493d3a7cd0fb129d52d