pgp: Move KeyserverResults to KeyserverSearch dialog

Niels De Graefrequested to merge
nielsdg/keyserver-results into main

Rather than us having a separate dialog for the results of key search, we can just use AdwNavigationView with 2 pages: first the initial search, and then a seoncd one that pops up to show the search results.

This is also quite a bit nicer from a UX point of view, as we no longer have several dialogs flashing when all of this is happening.

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