JS apps support 1/n

Summary:
### Connecting Flipper with JS apps by using electron's BrowserWindow and IPC

1. UI: there is a menu item in Devices tab which opens JS Emulator Launcher Sheet. Here we can configure URL to open and initial size of the window.
2. BrowserWindow, preloaded js: there is SupportJSClientPreload.js which initialize communication between flipper and app via electron's ipc
3. On flipper's side there is src/utils/js-client/serverUtils.tsx which contains most of JS emulator related code
4. Extracting of FlipperClientConnection: since we don't use RScocket to communicate with JS app I extracted needed methods to FlipperClientConnection (located in Client) and partly implemented them in JSClientFlipperConnection (requestResponse is just send a message now, doesn't return actual result)

Reviewed By: jknoxville

Differential Revision: D18572882

fbshipit-source-id: 56d1ca1a60ed2e51329b917021a09382cbb1ceec

src/App.tsx

@@ -19,6 +19,7 @@ import ShareSheetExportUrl from './chrome/ShareSheetExportUrl';
 import SignInSheet from './chrome/SignInSheet';
 import ExportDataPluginSheet from './chrome/ExportDataPluginSheet';
 import ShareSheetExportFile from './chrome/ShareSheetExportFile';
+import JSEmulatorLauncherSheet from './chrome/JSEmulatorLauncherSheet';
 import PluginContainer from './PluginContainer';
 import Sheet from './chrome/Sheet';
 import {ipcRenderer, remote} from 'electron';
@@ -34,6 +35,7 @@ import {
   ACTIVE_SHEET_SHARE_DATA_IN_FILE,
   ACTIVE_SHEET_SELECT_PLUGINS_TO_EXPORT,
   ACTIVE_SHEET_PLUGIN_SHEET,
+  ACTIVE_SHEET_JS_EMULATOR_LAUNCHER,
 } from './reducers/application';
 import {Logger} from './fb-interfaces/Logger';
 import BugReporter from './fb-stubs/BugReporter';
@@ -122,6 +124,8 @@ export class App extends React.Component<Props> {
       case ACTIVE_SHEET_PLUGIN_SHEET:
         // Currently unused.
         return null;
+      case ACTIVE_SHEET_JS_EMULATOR_LAUNCHER:
+        return <JSEmulatorLauncherSheet onHide={onHide} />;
       default:
         return null;
     }