Add support for cluster sharding persistence

[enashed]

Are there any plans to update this plugin to support cluster sharding persistence?

Currently if you use Akka.Persistence.MongoDB as a persistence plugin for cluster sharding, it fails to serialize messages. Even if you register the types using RegisterClassMap. You end up with an empty payload like this:

"Payload" : {
    "_t" : "ShardRegionRegistered"
}, 

In sql plugin, it uses binary serialisation to generate byte[], so hyperion serializer works fine with all those payloads. But in mongo, when BsonSerializer comes accross those messages:
ex: ShardRegionRegistered, ShardHomeAllocated, ShardHomeDeallocated, etc. It always generates an empty payload.

[Aaronontheweb]

closed via #42