(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

you should be able to configure the video path at build
time by passing --video_path=absolute_path
which will be played instead of displaying the LOGO

General polish for the page text.

Fixes #18.

Otherwise it's mixed state until we swipe carousel the first time or
press Next.

Use with_label() instead of a manually created label, make the headerbar
ones translatable, add mnenonics everywhere.

Take the position and round it, make the transition a bit more responsive.