MALItemListView: Don't commit changes to m_items until MAL reports success.

Before MALItems, we operated on a copy before setting it back in the
list view list. Now that we use shared_ptr, changes were being
propgated back sooner then my data model would like.

m_items is now shared_ptr<const Anime>; changes now require an
explicit copy.
configure.ac: Require sigc++ 2.2.11 so we can use C++11 lambdas with sigc