makes iteration on the UI slower

This is in preparation for a future gtk-rs release

* .page-body is indistinguishable from the default body style
* libadwaita uses .title-1, so .page-title can be swapped out
* .large-title was unused
* Other empty styles removed

We've had a few warnings sticking around for unused pieces
of code, or things that needed some form of error handling.

21df0c02 has lost the duration, but it was
longer than the carousel default. Reduce spring stiffness to have a longer
transition.

Because of an API change in libadwaita,
we need to use the latest version of
libadwaita-rs.

Temporarily bundles libadwaita, as the nightly
SDK doesn't have a new enough libadwaita because
we block the build.

This commit upgrades our rust dependencies and ports
Tour to libadwaita+GTK4. As part of porting we now use
GtkPicture instead of GtkImage, and AdwClamps to hold pages
in place.

This port is part of https://gitlab.gnome.org/GNOME/Initiatives/-/issues/26 and handles https://gitlab.gnome.org/GNOME/Initiatives/-/issues/32

Fixes https://gitlab.gnome.org/GNOME/gnome-tour/-/issues/36

- clean up unused pages
- add keyboard overview
- add search
- reword

Fixes https://gitlab.gnome.org/GNOME/gnome-tour/-/issues/41
Fixes https://gitlab.gnome.org/GNOME/gnome-tour/-/issues/42

tweak super key illustration

tweak super key illustration

"organise" is British English, which has its own separate locale. It's
not a valid spelling for use in user-visible strings.

(cargo-clippy lint tool)

Since we have a headerbar now and the first page is part
of the carousel, we shouldn't use HdyWindowHandle.

As per glib docs: `set_application_name`: Sets a human-readable name for the application.
This name should be localized if possible, and is intended for display to the user.

fixes #31

- avoid baloon duplicty

fixes #30

- Fullcolor tour
- Basic CSS keyframe animations
- Use of default grey backgrounds due to headerbar

Fixes https://gitlab.gnome.org/GNOME/gnome-tour/-/issues/29

The original implementation to determine the button opacity was clever,
but not easy to understand. The new implementation is more verbose,
but hopefully easier to get.

Anyhow was only used for paginator and
Option makes arguably more sense here than Result

closes #19