send simple invitation mail
fix: attendee properties
change status in database after send email
select already exists attendees for update them
update attendee and remove attende which is not in calendar more
chnge status after recaive REPLY
add status for EMAIL
fix problem with generate sql query
clean mail_handler
back to the future
add consts to caldav-PUT
wqMerge branch 'send_invitation_to_remote_attendee' into handle_remote_attendees

Conflicts:
	inc/caldav-PUT-functions.php
	scripts/mail_handler.php