Change the export file extension type

Summary: This diff imports and exports data in a `.flipper` file extension. This diff also adds the support to open flipper app by double clicking on the `.flipper` file.

Reviewed By: danielbuechele

Differential Revision: D14042846

fbshipit-source-id: 17e6b55bf2796d9abdf985411fce799600f7792b

src/MenuBar.js

@@ -326,7 +326,7 @@ function getTemplate(
               null,
               {
                 title: 'FlipperExport',
-                defaultPath: path.join(os.homedir(), 'FlipperExport.json'),
+                defaultPath: path.join(os.homedir(), 'FlipperExport.flipper'),
               },
               file => {
                 exportStoreToFile(file, store);