Rewrite skinny dialing to remove threaded simpleswitch

This rewrite changes skinny dialing from the threaded simpleswitch
to a scheduled timeout approach. There were some underlying issues
with the threaded simple switch with occasional corruption and
possible segfaults.

Review: https://reviewboard.asterisk.org/r/2240/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@378622 f38db490-d61c-443f-a65b-d21fe96a405b