Track favorites on a per-user basis

Currently, favorites are tracked at the cipher level. For org-owned ciphers,
this means that if one user sets it as a favorite, it automatically becomes a
favorite for all other users that the cipher has been shared with.

src/db/schemas/mysql/schema.rs

@@ -20,7 +20,6 @@ table! {
         notes -> Nullable<Text>,
         fields -> Nullable<Text>,
         data -> Text,
-        favorite -> Bool,
         password_history -> Nullable<Text>,
         deleted_at -> Nullable<Datetime>,
     }
@@ -55,6 +54,13 @@ table! {
     }
 }
 
+table! {
+    favorites (user_uuid, cipher_uuid) {
+        user_uuid -> Text,
+        cipher_uuid -> Text,
+    }
+}
+
 table! {
     folders (uuid) {
         uuid -> Text,