Enable SIP MESSAGE (RFC 3428) support by default

Few changes to configuration are required to enable out-of-box support of SIP MESSAGE method (RFC 3428) allowing messaging functionality for number of phones and softphones.

Add to general section of sip.conf

{noformat}
accept_outofcall_message = yes
outofcall_message_context = messages
auth_message_requests = no{noformat}

add to dialplan

{noformat}
[messages]
exten => _XXX,1,MessageSend(sip:${EXTEN},"${CALLERID(name)}"${MESSAGE(from)}){noformat}