application: load app menu from ui file
window: use a GtkHeaderBar and a gear menu
window: use a GtkStack instead of a GtkNotebook
bus: use a GtkSearchEntry instead of the filter box
bus: add margins to the bus box
introspection: use a 'reload' image button instead of a text button
build: don't use AM_GNU_GETTEXT

AM_GNU_GETTEXT can no longer be used with IT_PROG_INTLTOOL.

Same problem/fix as https://bugzilla.gnome.org/show_bug.cgi?id=706828;
see https://bugzilla.gnome.org/show_bug.cgi?id=705365#c7 for more
details.

https://bugzilla.gnome.org/show_bug.cgi?id=709203
window: allow closing currently visible bus
window: keep track of whether Session and System bus are already open

And just don't allow opening them again if they are already there.
build: update ignored files