res_fax: Provide AMI equivalents for fax CLI commands

Specifically the following equivalents were created:
fax show session -> FAXSession
fax show sessions -> FAXSessions
fax show stats -> FAXStats

Review: https://reviewboard.asterisk.org/r/3666/


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@418911 f38db490-d61c-443f-a65b-d21fe96a405b