Made GtkIconView reset the context and invalidate all sizes when a row changes.

Made GtkIconView reset the context and invalidate all sizes when a row changes.

GtkIconView should have a "grow-only" mode to handle optimization to
only allow icons to grow in width when rows change, however since
GtkIconView still does not handle large numbers of rows for now we'll
just relayout the whole thing whenever a series of rows change.

Also fixed up to watch the context incase of implicit resets.