* Switch build system from Autotools to Meson (and remove Autotools).
* Update the license from GPLv2+ to GPLv3+.
* Clear separation between the library and the app: move library to its own
directory (still in the same git repo), split some source files in two,
correctly handle GSettings in the library, and in the app use only really
public libdevhelp APIs.
* Add a profile infrastructure in the library, for example to have a generic
profile and a GNOME profile in the future.
* Overhaul preferences dialog implementation.
* Use the Amtk library to create the menus and the GtkShortcutsWindow. It
permits to avoid information duplication, and will permit to provide a
higher-level libdevhelp API.
* A few other small improvements.
* Translation updates.
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