LibCore: Put all classes in the Core namespace and remove the leading C

I've been wanting to do this for a long time. It's time we start being
consistent about how this stuff works.

The new convention is:

- "LibFoo" is a userspace library that provides the "Foo" namespace.

That's it :^) This was pretty tedious to convert and I didn't even
start on LibGUI yet. But it's coming up next.

Servers/AudioServer/ASClientConnection.cpp

@@ -48,7 +48,7 @@ void ASClientConnection::for_each(Function<void(ASClientConnection&)> callback)
         callback(connection);
 }
 
-ASClientConnection::ASClientConnection(CLocalSocket& client_socket, int client_id, ASMixer& mixer)
+ASClientConnection::ASClientConnection(Core::LocalSocket& client_socket, int client_id, ASMixer& mixer)
     : IClientConnection(*this, client_socket, client_id)
     , m_mixer(mixer)
 {