doesn't compile, but UI.h/.cpp code has been divvy'd up.

refs #43 @2h

src/UIDrawable.cpp

@@ -0,0 +1,13 @@
+#include "UIDrawable.h"
+
+UIDrawable::UIDrawable() { click_callable = NULL;  }
+
+void UIDrawable::click_unregister()
+{
+    click_callable.reset();
+}
+
+void UIDrawable::render()
+{
+    render(sf::Vector2f());
+}