Interact with key views instead of with underlying models

This ensures that the key views (which keep track of the keys independent
of the models) return the correct lists of keys so that we can use the
simpler API of the key views.

(cherry picked from commit 54f23ccc7b7db45ed89b4d8e0142a6d8a1d24d0a)

• GnuPG-bug-id: T7963