LibCore: Add CLocalServer, a server-only local socket class.

Instead of trying to support both client and server in CLocalSocket, let's
have a specialized server class.

The basic usage is:

    CLocalServer server;
    server.listen("/tmp/name-of-portal");
    server.on_ready_to_accept = [&] {
        CLocalSocket* client = server.accept();
        ...
    };

This will make things a lot simpler, since an accepting socket doesn't need
half of the stuff that a regular CIODevice provides. :^)

Libraries/LibCore/Makefile

@@ -7,6 +7,7 @@ OBJS = \
     CFile.o \
     CSocket.o \
     CLocalSocket.o \
+    CLocalServer.o \
     CTCPSocket.o \
     CElapsedTimer.o \
     CNotifier.o \