remove window dependency

Summary:
Fixes required to be able to run Flipper in node.js:
* Adds checks if the `window`-object exists before using it, to allow running in node.
* Imports from within Flipper should directly reference the file they are requiring instead of `import from 'flipper'`. This was done in most of the places. Fixed a few occurrences where this wasn't the case. This is to prevent cyclic dependencies in node.
* shared packages (React, ReactDOM and Flipper) were exposed on the `window` before, changed this to `global` as this works in browser and node.
* Adds some missing methods to our electron stubs (used for testing and headless Flipper)

Reviewed By: passy

Differential Revision: D13786577

fbshipit-source-id: 145d560f1446e7d0bdec2acd8dd54dae983d7b36

src/dispatcher/iOSDevice.js

@@ -46,9 +46,12 @@ function forwardPort(port: number, multiplexChannelPort: number) {
 const portForwarders: Array<ChildProcess> = GK.get('flipper_ios_device_support')
   ? [forwardPort(8089, 8079), forwardPort(8088, 8078)]
   : [];
-window.addEventListener('beforeunload', () => {
-  portForwarders.forEach(process => process.kill());
-});
+
+if (typeof window !== 'undefined') {
+  window.addEventListener('beforeunload', () => {
+    portForwarders.forEach(process => process.kill());
+  });
+}
 
 function queryDevices(store: Store, logger: Logger): Promise<void> {
   const {connections} = store.getState();