Terminal+LibGUI: Make the terminal cursor blink.

Added a GTimer class to help with this. It's just a simple GObject subclass
that sets up an event loop timer and invokes a callback on timeout.

LibGUI/GTimer.cpp

@@ -0,0 +1,39 @@
+#include <LibGUI/GTimer.h>
+
+GTimer::GTimer(GObject* parent)
+    : GObject(parent)
+{
+}
+
+GTimer::~GTimer()
+{
+}
+
+void GTimer::start()
+{
+    start(m_interval);
+}
+
+void GTimer::start(int interval)
+{
+    if (m_active)
+        return;
+    start_timer(interval);
+    m_active = true;
+}
+
+void GTimer::stop()
+{
+    if (!m_active)
+        return;
+    stop_timer();
+    m_active = false;
+}
+
+void GTimer::timer_event(GTimerEvent&)
+{
+    if (m_single_shot)
+        stop();
+    if (on_timeout)
+        on_timeout();
+}