Userland: Rename Core::Object to Core::EventReceiver

This is a more precise description of what this class actually does.

Userland/Libraries/LibCore/UDPServer.cpp

@@ -21,8 +21,8 @@
 
 namespace Core {
 
-UDPServer::UDPServer(Object* parent)
-    : Object(parent)
+UDPServer::UDPServer(EventReceiver* parent)
+    : EventReceiver(parent)
 {
 #ifdef SOCK_NONBLOCK
     m_fd = socket(AF_INET, SOCK_DGRAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0);