Focus next face

Just a tiny improvement. When assigning names to faces in the "albums" view (not "people" view), it can be helpful that the next face is focused when you assigned a name to another face. This commit implements that the lineEdit of a random face is focused whenever a name was assigned to face in the picture. Thus, you can assign multiple names to faces with just using the keyboard in the "people" view (an additional click in the next lineEdit is obsolete).