Implement event loop timers.

GObjects can now register a timer with the GEventLoop. This will eventually
cause GTimerEvents to be dispatched to the GObject.

This needed a few supporting changes in the kernel:

- The PIT now ticks 1000 times/sec.
- select() now supports an arbitrary timeout.
- gettimeofday() now returns something in the tv_usec field.

With these changes, the clock window in guitest2 finally ticks on its own.

AK/HashMap.h

@@ -83,6 +83,11 @@ public:
         return find(key) != end();
     }
 
+    void remove(IteratorType it)
+    {
+        m_table.remove(it);
+    }
+
 private:
     HashTable<Entry, EntryTraits> m_table;
 };