adding jest test setup

Summary:
Adds a test runner for jest test and adds three simple test cases:
- render the app
- start a server
- client connecting to the app

Test can be run using `yarn test`.

To make the test runner work, some changes needed to be made:
- remove the export of `init()` from `'flipper'`, because it was a cyclic dependency
- updating Button.js to the new ref-API

Reviewed By: jknoxville

Differential Revision: D10027078

fbshipit-source-id: 49107b0dd4dec666b92ecd841422fe7e6b3a7756

flow-typed/npm/redux-mock-store_vx.x.x.js

@@ -0,0 +1,46 @@
+// flow-typed signature: 0ce56690a743910f5934d0ffc0f26d61
+// flow-typed version: <<STUB>>/redux-mock-store_v1.5.3/flow_v0.76.0
+
+/**
+ * This is an autogenerated libdef stub for:
+ *
+ *   'redux-mock-store'
+ *
+ * Fill this stub out by replacing all the `any` types.
+ *
+ * Once filled out, we encourage you to share your work with the
+ * community by sending a pull request to:
+ * https://github.com/flowtype/flow-typed
+ */
+
+declare module 'redux-mock-store' {
+  declare module.exports: any;
+}
+
+/**
+ * We include stubs for each file inside this npm package in case you need to
+ * require those files directly. Feel free to delete any files that aren't
+ * needed.
+ */
+declare module 'redux-mock-store/lib/index' {
+  declare module.exports: any;
+}
+
+declare module 'redux-mock-store/test/index' {
+  declare module.exports: any;
+}
+
+declare module 'redux-mock-store/test/mock/middleware' {
+  declare module.exports: any;
+}
+
+// Filename aliases
+declare module 'redux-mock-store/lib/index.js' {
+  declare module.exports: $Exports<'redux-mock-store/lib/index'>;
+}
+declare module 'redux-mock-store/test/index.js' {
+  declare module.exports: $Exports<'redux-mock-store/test/index'>;
+}
+declare module 'redux-mock-store/test/mock/middleware.js' {
+  declare module.exports: $Exports<'redux-mock-store/test/mock/middleware'>;
+}