userpage: implement login message card

Shares code with custom emails, so most related functions have had a
%s/Email/Message/g. Press the edit button on the user page setting to
add a message.

lang/admin/en-us.json

@@ -113,7 +113,9 @@
         "actions": "Actions",
         "searchOptions": "Search Options",
         "matchText": "Match Text",
-        "jellyfinID": "Jellyfin ID"
+        "jellyfinID": "Jellyfin ID",
+        "userPageLogin": "User Page: Login",
+        "userPagePage": "User Page: Page"
     },
     "notifications": {
         "changedEmailAddress": "Changed email address of {n}.",
@@ -209,4 +211,4 @@
             "plural": "Extended expiry for {n} users."
         }
     }
-}
+}