If the Loader size is set explicitly we can set the item size
before the bindings are run, and avoiding an additional
anchor layout.

Also ensure item implict size changes are propagated/notified in the
Loader.

Change-Id: Ie22b018b22be8457ccf30b907a26e44260b9cef7
Reviewed-by: Michael Brasser <michael.brasser@nokia.com>