Add ability for modules to dynamically register logger levels

Add ability for modules to dynamically register logger levels

This patch adds the ability for modules to dynamically create logger levels for their own use; these are named levels just like the built-in levels, and can be directed to any destination that the logger can send any level to, by including their names in logger.conf.

Review: https://reviewboard.asterisk.org/r/244/

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@194610 65c4cc65-6c06-0410-ace0-fbb531ad65f3