Let the contact list be resized, and give the contact the rest of the page

The contacts grid still had three columns from when the address books sat
inside the view: 220px for them, 280-360px for the list, the rest for the
contact. The books moved to the app's left pane in 350f4f4 and the grid
never followed, so the list was squeezed into the books' 220px, truncating
names, the contact was held to 360px, and the remaining width sat empty.

It is two columns now, with the same splitter as the message list between
them: drag between 240px and the width that leaves 360px for the contact,
arrow keys move it, double-click puts it back to 320px. The width is a
device setting beside the mail list's, so it is kept by a device marked as
your own and never synced. The splitter is hidden where contacts show one
pane at a time. The unused .contacts-books rules are gone.

"Resize contact list" is in all nine catalogues.

web/src/locales/de.ts

@@ -1215,6 +1215,7 @@ export const catalog: Catalog = {
     "Full screen": "Vollbild",
     "Resize panes": "Bereichsgröße ändern",
     "Resize message list": "Größe der Nachrichtenliste ändern",
+    "Resize contact list": "Größe der Kontaktliste ändern",
     "Resize sidebar": "Größe der Seitenleiste ändern",
     "Hide from list": "Aus der Liste ausblenden",
     "Show in list": "In der Liste einblenden",