retail: calls between DDIs of the same Retail client shouldn't be tarificated

[Kaian]

Right now, calls from retail accounts to one of the DDIs of the same Retail Clients are bounced in ProxyTrunks (generating CDR entries) which makes these call tarificable.

It would be required to evaluate if retail account outgoing calls should be routed through a retail account within the same client without using proxy trunks.

Prior to this, we should implement #89 so the numbers are already standarized and not transformations are required in the route.

[cruzccl]

Call between DDIs of the same vPBX client shouldn't be tarificated neither.