* GtkBox isn't meant to be subclassed, and apps should not do it.
Instead they should subclass AdwBin or GtkWidget depending on their
use case.

* The main reason we were using GtkBox was to contain our header
and our content. Now we use AdwToolbarView for that purpose.

This only leaves us with only one translatable string defined on a rust file,
due to the low gettext/rust support...

Fixes #34

Fixes #32

It is nowadays similar to the ImagePageWidget, so let us just use that

It is no longer used and if we ever re-add it, we can think of another way
to do that.

Instead of doing multiple overlays, do a single overlay containing all
buttons as type=overlay children. This makes the carousel span the
window from start to end.

This allow us to simplify the changes on the UI part

This would allow us to construct the pages on the ui files later

it doesn't make much sense now, but it will do once we port the rest of widgets as well

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