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/WindowServer/WSClientConnection.cpp

@@ -65,7 +65,7 @@ WSClientConnection* WSClientConnection::from_client_id(int client_id)
     return (*it).value.ptr();
 }
 
-WSClientConnection::WSClientConnection(CLocalSocket& client_socket, int client_id)
+WSClientConnection::WSClientConnection(Core::LocalSocket& client_socket, int client_id)
     : IClientConnection(*this, client_socket, client_id)
 {
     if (!s_connections)