Add Event Registry/REST types

Caveat, I am not super familiar with this area,s till.  My point is that the word and concept of etcd should never appear here.

struct registry should be defined as something like 

    {
        RegsitryBackingStore
        ttl int
    }

Where BackingStore is an interface with functions that map to Etcd.  Creating a registry should be something like:

    backingStore := NewEtcdBackingStore()
    ....
    eventRegistry:      event.NewRegistry(backingStore, uint64(c.EventTTL.Seconds())),