Introduce NUX element

Summary:
allow-large-files

This diff introces the `NUX` element that can be wrapped around any other element to give a first-time usage hint.

Hint dismissal is stored by taking a hash of the hint contents, and scoped per plugin.

Users can reset the 'read' status in the settings page

Example usage:

```
<NUX
  title="Use bookmarks to directly navigate to a location in the app."
  placement="right">
  <Input addonAfter={<SettingOutlined />} defaultValue="mysite" />
</NUX>
```

Reviewed By: nikoant

Differential Revision: D24622276

fbshipit-source-id: 0265634f9ab50c32214b74f033f59482cd986f23

desktop/app/src/init.tsx

@@ -34,6 +34,7 @@ import {PopoverProvider} from './ui/components/PopoverProvider';
 import {initializeFlipperLibImplementation} from './utils/flipperLibImplementation';
 import {enableConsoleHook} from './chrome/ConsoleLogs';
 import {sideEffect} from './utils/sideEffect';
+import {NuxManagerContext, createNuxManager} from 'flipper-plugin';
 
 if (process.env.NODE_ENV === 'development' && os.platform() === 'darwin') {
   // By default Node.JS has its internal certificate storage and doesn't use
@@ -56,7 +57,9 @@ const AppFrame = () => (
       <ContextMenuProvider>
         <Provider store={store}>
           <CacheProvider value={cache}>
-            <App logger={logger} />
+            <NuxManagerContext.Provider value={createNuxManager()}>
+              <App logger={logger} />
+            </NuxManagerContext.Provider>
           </CacheProvider>
         </Provider>
       </ContextMenuProvider>