Set up Flipper decapitated packages

Summary:
This diff introduces the packages necessary for Flipper decapitated.

* flipper-common: utilities & types shared between client, server, flipper-plugin
* flipper-server-core: all device & client management goes in here. Basically flipper's backend
* flipper-ui-core: all UI goes in here, as far as it doesn't depend on Electron
* desktop: the Electron app, will load server-core and ui-core, and glue them together, providing implementations for some electron specific stuff like dialgos
* flipper-server: A node process hosting flipper-server-core, that can be connected to over websockets. And probably can serve a browser version of the UI as well.
* flipper-ui-browser: thin wrapper around flipper-ui-core, providing some browser specific behavior / stubs.
* flipper-dump: (might remove later), but want to hack a quick and dirt flipper dump in here, as alternative way to test flipper-server-core.

This diff just creates the packages, but doesn't move any code, so it can be summarized as:

restoftheowl

Reviewed By: nikoant

Differential Revision: D30218646

fbshipit-source-id: 735598a1261a98e584f52504b5eba01ec0afa162

desktop/app/src/init.tsx

@@ -51,6 +51,9 @@ import {getVersionString} from './utils/versionString';
 import {PersistGate} from 'redux-persist/integration/react';
 // eslint-disable-next-line flipper/no-electron-remote-imports
 import {ipcRenderer, remote} from 'electron';
+import {helloWorld} from 'flipper-server-core';
+
+helloWorld();
 
 if (process.env.NODE_ENV === 'development' && os.platform() === 'darwin') {
   // By default Node.JS has its internal certificate storage and doesn't use