Redo this series of examples from 2013, and adapt it to modern
way of doing things. The biggest differences are that we use
a headerbar right from the start, and don't mention the app
menu.
Fixes: #2730
This merged gtk, gdk and gsk into one library, making it possible to
have internal private APIs between gtk them, as well as producing more
efficient code.
https://bugzilla.gnome.org/show_bug.cgi?id=773100
Setting up the icon and desktop file is a pretty central part
of making an application work, so we should do it for our example.
The fact that the examples are uninstalled makes this a little
more complicated.
Add a new example to the getting started part of the docs. The focus
of this example is on 'new stuff': GtkApplication, templates, settings,
gmenu, gaction, GtkStack, GtkHeaderBar, GtkSearchBar, GtkRevealer,
GtkListBox, GtkMenuButton, etc.
It is being developed in several steps. Each step is put in a separate
directory below examples/: application1, ..., application8. This is a
little repetitive, but lets us use the code of all examples in the
documentation.
