update: add all categories in metadata files to repo definitions

!1366 makes it so categories are now defined by the repo. Categories can be
defined in the config so that lint has a list of categories to enforce. This
also provides a place for localization and icons for the categories. The old
way of defining categories was just listing them in app metadata files. This
restores that way of functioning when using index-v2.

closes #1137

tests/repo/index-v2.json

@@ -533,7 +533,10 @@
         "name": {
           "en-US": "System"
         }
-      }
+      },
+      "1": {},
+      "2.0": {},
+      "tests": {}
     },
     "requests": {
       "install": [
@@ -1443,4 +1446,4 @@
       }
     }
   }
-}
+}