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.
1. Remove set_icons property
2. Make it a GtkWidget subclass
3. Add gtk_fishbowl_set_creation_func()
4. Make the widgetbowl use the new benchmarking infrastructure of the
fishbowl
We now properly use GdkFrameTimings and can therefor check for dropping
even a single frame in the history (of 16 frames or 1/4 of a second).
Once that happens, we immediately stop adding new items to the bowl.
A side effect is that the number of icons is now a *lot* smaller.
And have a priv->display instead of a priv->screen.
Includes turning gtk_menu_set_screen() into gtk_menu_set_display(),
because that function just forwards to its window.
