Adding core component

This might need to be lifted and shifted into ElasticMQ core itself at a later
time if it's worth the bother.
Adding representation for Topic entities
Adding TopicManagerActor

The idea is that this class will eventually co-ordinate fan out to other
actors, though I may have to essentially include SQS actors here so that you
can create queues and topics in the same "space"
If I had a dollar for every time I failed at copy and paste so far...