core: notifs can now have a custom icon and be clickable: - new host.doAction method, to open a specific widget/target (chat only for now) - when adding a notif, symbol can now be specified - an action can be linked to a notification - notifs design improvments - plugins contact list and chat use the new doAction/notif action - if None is given as old widget in SwitchWidget, the new getWidgetToSwitch method is used to select one to switch.