Make Client initialize server add-ons

Reviewed By: mweststrate

Differential Revision: D34044353

fbshipit-source-id: 99bcb1559787b2a904bdd796233666a7a4783ea4

desktop/flipper-common/src/index.tsx

@@ -17,6 +17,7 @@ export {
   NoopLogger,
 } from './utils/Logger';
 export * from './server-types';
+export * from './ServerAddOn';
 export {sleep} from './utils/sleep';
 export {timeout} from './utils/timeout';
 export {isTest} from './utils/isTest';