Implement poor man's invitation via Organization invitation

src/db/schema.rs

@@ -113,6 +113,12 @@ table! {
     }
 }
 
+table! {
+    invitations (email) {
+        email -> Text,
+    }
+}
+
 table! {
     users_collections (user_uuid, collection_uuid) {
         user_uuid -> Text,