Added test case to assert all object types finalize properly.

The test case uses a weak ref to assert objects can finalize,
and then spins the main loop shortly after finalizing to assert
that the finalized object did not leak GSources into the main context
causing latent crashes.
wayland: Implement gdk_keymap_get_entries_for_keycode
wayland: Implement more keymap functions

This commit implements gdk_keymap_get_entries_for_keyval
and gdk_keymap_lookup_key.
objects-finalize test: Blacklist gdk_pixbuf_simple_anim_iter_get_type()
Updated kn translations
broadway: Fix warning

Don't pass NULL source_device in grab/ungrab events
broadway: Unsure we clear the grab on window hide
Updated kn translations
reftests/Makefile.am: remove whitespace following trailing backslash
GdkOffscreenWindow: Implement gdk_window_get_frame_extents()

This avoids crashes in gtk_window_get_position() whenever the GdkWindow
is offscreen.
gtk-demo: Remove multiscreen support

There's only one screen per display, so no need to let users select from
a list of that 1 screen.
icontheme: Remove unused function
gtk: Simplify code for reduced screen count
x11: Simplify code for single-screen case
gdk: Deprecate gdk_display_get_n_screens()
testgtk: Get rid of screen part in display & screen test
tests: Remove testmultiscreen example

There aren't multiple screens anymore, so no need to test that.

Multiple displays can be tested with gtk-demo and testgtk.
tests: Remove multiscreen code from teststusicon
reftests: Add a test for window default size

https://bugzilla.gnome.org/show_bug.cgi?id=697275
gtk_recent_chooser_set_filter: Allow NULL value to unset the filter.

While GtkRecentChooser implementations accept for the "filter" property
to unset the current filter, the API fires an unneeded assertion.

This patch removes the assertion.