Add prinotify messages to skinny.

Adds both fixed and variable prinotify messages and clearprinotify messages to skinny.
Also adds cli function for pushing messages to devices. i

Initial code by snuffy, expanded by myself to include fixed messages.

(closes issue ASTERISK-21091)
Reported by: snuffy
Tested by: snuffy, myself
Patches:
    skinny-prinotify02.diff uploaded by wedhorn (license 5019)

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@382007 65c4cc65-6c06-0410-ace0-fbb531ad65f3