Add SSE

[gedw99]

To allow service in client and server to push CDC updates when data sources change.

Create, Update, Delete are the ops.

namespace topic that maps to json fragment is the scope of the payload.

client will then update cache of json using that scope.

later when templates are introduced these can also be pushed. Just need CDC on server file system. At the moment html templates are not used. Scoping it a xml scope instead of json obviously.