contact-widget: use the day-selected sig to update birthday
contact-widget: use the day-selected sig to update birthday

Having to double click on a day to update it was really confusing and most
people (including me!) were just thinking that was not working.

GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets