Load attention and overlay pixmaps from item properties, watch the
corresponding update signals, and prefer attention artwork while an item is in
NeedsAttention state.
When an item only exports an attention movie asset, fall back to loading that
asset as a static pixbuf so the tray still shows the alert state.
Signed-off-by: Austin Horstman <khaneliman12@gmail.com>
f6d92fd708