Add the names of the main widgets as keywords to
our demos, but also things like "game". This helps
finding relevant demos in our growing list. You
can now for example type "label", and find the
"error states" and "links" demos showing GtkLabel
features.
Change the apis in GtkListView, GtkColumnView and
GtkGridView to be explicitly about GtkSelectionModel,
to make it obvious that the widgets handle selection.
Update all users.
We're a normal application, so we can use the normal way to hook up code
into builder files, which is using dlsym() for the function pointers.
There's no need to to extra work exporting static symbols.
gtk_builder_connect_signals() is no longer necessary, because all the
setup that made it necessary to have this extra step is now done
automatically via the closure functions.
This is pretty unused and gets in the way of the next steps.
A potential side effect is that for templates the widget was passed as
the user data argument. If that turns out to be important, we have to
special case that situation.