Convert plugin.js to plugin.tsx

Summary:
* Deletes plugin.js
* Adds plugin.tsx
* Adds plugin flow-typed module that has the old flow types

Reviewed By: passy

Differential Revision: D16668067

fbshipit-source-id: b2f0ce47c4cf7125b4e352821e921b97675d12a9

src/dispatcher/__tests__/plugins.electron.js

@@ -13,7 +13,7 @@ import dispatcher, {
 } from '../plugins';
 import path from 'path';
 import {remote} from 'electron';
-import {FlipperPlugin} from '../../plugin';
+import {FlipperPlugin} from '../../plugin.tsx';
 import reducers from '../../reducers/index.tsx';
 import {init as initLogger} from '../../fb-stubs/Logger.js';
 import configureStore from 'redux-mock-store';