Add AuditModule which showcases ActorRef injection

I took a stab at injecting ActorRef into Actors since this was requested at least couple of times.

Changes include
* inject using Named and Binding annotations
* use prototype and singleton scopes
* update dependencies to latest and to scala 2.11
Since `AuditCompanion` "depends on" `AuditBus` via dependency injection, should we keep the dependencies non-circular by moving the `AuditEvent` case class into `object AuditBus`? That way class `AuditBus` will not need to `import AuditCompanion._`. WDYT?