* Make sure all source files have a LGPL copyright header, and standardize
non-standard variations of the header to a common form.
* Check and update all copyright notices.
* Remove 'Written By:' lines. They are universally incomplete and
typically indicate only who started a particular file.
https://bugzilla.gnome.org/show_bug.cgi?id=634550
Add StWidget:can-focus, st_widget_navigate_focus(), and
st_container_get_focus_chain(), and implement as needed to allow
keyboard navigation of widgets.
https://bugzilla.gnome.org/show_bug.cgi?id=621671
Add StContainer, which implements the ClutterContainer interface based
on the container methods in st-private and make the existing containers
subclass it.
https://bugzilla.gnome.org/show_bug.cgi?id=613907
