Add serviceURL stuff to skinny.

Patch adds all the packet and structure stuff to skinny to enable setting 
service URLs in skinny, such as corporate directories.

This stuff is only relevant during load/unload as when activated. Also 
some minor changes removing duplicated counting of addons and speedials in 
handle_skinny_show_devices.

Review: https://reviewboard.asterisk.org/r/2321/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@381718 65c4cc65-6c06-0410-ace0-fbb531ad65f3