WIP: normal bug EXT-6865 (Voice isn't blocked for Avaline callers connected via PSTN bridge)

Applyied Aimee's patch to enable blocking of avaline caller:
 added an "External" mute type which isn't sent to the SL servers or stored in the cache across sessions.
 The caller's ID will change each time so there's no point cluttering up the mute list by persisting them.

Known issue: Right now the mute is added with the caller's phone number as the name shown in the block list,
 so that will need changing to "Avaline Caller 1" etc

--HG--
branch : product-engine