Add annotations and fix minor bugs with mappers

Admin/Install/db.json

@@ -33,6 +33,11 @@
                 "name": "exchange_website",
                 "type": "VARCHAR(255)",
                 "null": false
+            },
+            "exchange_version": {
+                "name": "exchange_version",
+                "type": "VARCHAR(50)",
+                "null": null
             }
         }
     }