Adds capability to select plugins for which the data would be exported

Summary: This diff adds `selectedPlugins` property in the redux store. With this diff now you can pass the list of plugins to headless so that it exports only the selected plugin's data

Reviewed By: passy

Differential Revision: D16280167

fbshipit-source-id: b03a1c49a7f51547470e0bcfa43083e52efabdd0

src/utils/__tests__/pluginUtils.node.js

@@ -30,6 +30,7 @@ function mockPluginState(
     gatekeepedPlugins,
     disabledPlugins,
     failedPlugins,
+    selectedPlugins: [],
   };
 }