Merged Neil's fix-places-memleaks branch after review and approval. Fixes
numerous mem-leaks in Places and Quicklists.

modified:
  unity-private/launcher/quicklist-check-menu-item.vala
  unity-private/launcher/quicklist-image-menu-item.vala
  unity-private/launcher/quicklist-menu-item.vala
  unity-private/launcher/quicklist-radio-menu-item.vala
  unity-private/places/places-default-renderer-group.vala
  unity-private/places/places-default-renderer-tiles.vala
  unity-private/places/places-default-renderer.vala
  unity-private/places/places-place-home-renderer.vala
  unity-private/places/places-place-search-entry.vala
  unity-private/places/places-view.vala
  unity/unity-layered-bin.vala