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.

Meta/Lagom/SimpleIPCClient.cpp

@@ -47,7 +47,7 @@ public:
 
 int main(int, char**)
 {
-    CEventLoop event_loop;
+    Core::EventLoop event_loop;
 
     SimpleIPCClient client;
 

Meta/Lagom/SimpleIPCServer.cpp

@@ -37,7 +37,7 @@ class SimpleIPCServer final :
 
     C_OBJECT(SimpleIPCServer)
 public:
-    SimpleIPCServer(CLocalSocket& socket, int client_id)
+    SimpleIPCServer(Core::LocalSocket& socket, int client_id)
         : ConnectionNG(*this, socket, client_id)
     {
     }
@@ -50,10 +50,10 @@ public:
 
 int main(int, char**)
 {
-    CEventLoop event_loop;
+    Core::EventLoop event_loop;
 
     unlink("/tmp/simple-ipc");
-    auto server = CLocalServer::construct();
+    auto server = Core::LocalServer::construct();
     server->listen("/tmp/simple-ipc");
     server->on_ready_to_accept = [&] {
         auto client_socket = server->accept();

Meta/Lagom/TestApp.cpp

@@ -30,9 +30,9 @@
 
 int main(int, char**)
 {
-    CEventLoop event_loop;
+    Core::EventLoop event_loop;
 
-    auto timer = CTimer::construct(100, [&] {
+    auto timer = Core::Timer::construct(100, [&] {
         dbg() << "Timer fired, good-bye! :^)";
         event_loop.quit(0);
     });