db_settings bug fixes & unlock_db redesign

Continuation of https://gitlab.gnome.org/World/PasswordSafe/-/merge_requests/566.

This turned into a bit of a rabbit hole, which required some changes in unlock_database. Since that code was full of little issues I decided to simplify it by removing the stack and handling it as a single case, this has been discused many times.

cc @bertob the entry is requesting a width of 250px, it is a bit smaller than before, any opinions on the design? It is using AdwStatusPage and the vertical margins are as small as the widget allows for it. For comparison here is stable: