* hildon/hildon-banner-private.h: Add a GtkAlignment to the private
structure.
* hildon/hildon-banner.c (hildon_banner_init): Use a GtkAlignment
to ensure the banner contents are centered, instead of relying on
the expand and fill properties in GtkHBox.
(hildon_banner_ensure_child): Do not expand nor fill the child widget.
Fixes: NB#108265 (Animation banner not properly centered)