keyboard: Fix compile warning

We need to include gnome-languages
goa: Sync code to be closer to g-c-c panel

This also eliminates some compiler warnings
Sync network-dialogs.c from g-c-c
copy-worker: Remove g_type_init()
assistant-gtk: Use GTK_STACK_TRANSITION_TYPE_SLIDE_LEFT_RIGHT
assistant: Remove assistant subclasses

We used to have GTK+ and Clutter-based assistants, but now that
GtkStack is out, we can simply only have one.
gis-assistant: Remove the intermediate frame

This was really only a placeholder widget
gis-assistant: Remove the page action widget area

We no longer use action widgets.
gis-assistant: Use composite widget templates