* Asterisk app: add IAX2 peer graphs
* It's an entirely new graph and will not break existing graphs.
* The asterisk extend script must be updated to provide the appropriate poller data.
* The PR for librenms-agent/snmp/asterisk is here: https://github.com/librenms/librenms-agent/pull/274
* code climate, round 1
* clarified unit text
* code climate, round 2
* changes needed to properly generate test data
* linux_asterisk-v1 test data
