Tracking interactions

Summary:
Set up basic primitives for user interaction tracking. I hope the docs and unit tests in this diff are self explanatory :)

In upcoming diffs:
* Wire up to scuba events
* Annotate all important parts of Flipper Chrome
* Investigate if we can wrap important interactions of ANT by default

Reviewed By: jknoxville

Differential Revision: D25120234

fbshipit-source-id: 9849d565d7be27e498cc2b4db33e7d6e6938ee06

desktop/flipper-plugin/src/__tests__/api.node.tsx

@@ -29,14 +29,18 @@ test('Correct top level API exposed', () => {
       "Layout",
       "NUX",
       "TestUtils",
+      "Tracked",
+      "TrackingScope",
       "batch",
       "createState",
       "produce",
       "renderReactRoot",
+      "sleep",
       "styled",
       "theme",
       "usePlugin",
       "useValue",
+      "withTrackingScope",
     ]
   `);