Tidy up of the client interface code - more commonly known as the
"right hand side of the server". Right since the start the filter
side of the server has been nice and tree like - every Filter sent
data to another Filter. At the top of the tree there was a "special"
Filter known as the RootFilter, which to the other Filters just
looked like a normal Filter. This was nice, and simple, and expandable.

The Client Interface on the other hand was messy. The root filter
had some hacky wrapper threads which pulled from a queue and pushed
to the relevant client interfaces (one for real time stuff, and the
other for databases). There was no simple room for expandability -
it was all hardwired to do just what was needed at the time.

This commit changes that. A Client Interface now connects to another
Client Interface, with a special one being found in the RootFilter
(yes, maybe that needs a name change now :-). So we can chain client
interfaces, and move other bits and bobs around in the server - for
example, alerting no longer needs to be connected to the Client
Interface, it can connect straight to the RootFilter (or, wherever
the config tells it ;).

Hopefully this sanitizes the underlying layout of the server a bit.

As a final note, I dropped the DBInterface. This used to insert
data in to a MySQL database. We've long since stopped using that,
and it's fallen behind and is way out of date. For now, it's gone
in to the attic.