Use a separate icon image as a drag actor instead of using the clone of the icon

Use a separate icon image as a drag actor instead of using the clone of the icon

Clutter no longer allows using a clone of an actor that is not a part of
the scene graph. This is what used to happen when we created a clone for
the icon of the item that was being dragged, and then closed the More panes
with the original item, removing the icon from the scene graph. This was
also when happened when the user hit Esc while dragging, which prompted the
overlay to close, removing the original icon from the scene graph.

Rename getIcon() methods to createIcon() to better reflect on the fact that
a new icon is created each time the method is called (we do use cache in
some cases).

Remove a stray log message in overlay.js

Fixes http://bugzilla.gnome.org/show_bug.cgi?id=585490
and http://bugzilla.gnome.org/show_bug.cgi?id=585489