gnome-shell: item: make function public

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
gnome-shell: move some update handling from item to indicator

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
gnome-shell: move more update handling from item to indicator

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
gnome-shell: move all update handling to indicator

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
gnome-shell: indicator: rename var

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>