test-ui: Show content changes in statusbar
test-ui: Show content changes in statusbar

Add toggle option to activate content changes notification in plugins, showing
the changes happening in status bar.

Signed-off-by: Juan A. Suarez Romero <af79b5692270b306571bb1d8bbe0285ae3ac93d9@igalia.com>

grilofw/grilo,kyoushuu/grilo,jasuarez/grilo,grilofw/grilo,GNOME/grilo,MathieuDuponchelle/grilo,MathieuDuponchelle/grilo,MathieuDuponchelle/grilo,GNOME/grilo,jasuarez/grilo,grilofw/grilo,kyoushuu/grilo,kyoushuu/grilo,jasuarez/grilo,kyoushuu/grilo