app: add export route

Currently, the export route only creates the snapshot (the other side
of in-place import). In the future, the export route can export to a
custom backup config (like import).

src/routes/apps.js

@@ -8,6 +8,7 @@ exports = module.exports = {
     uninstall,
     restore,
     importApp,
+    exportApp,
     backup,
     update,
     getLogs,
@@ -443,6 +444,17 @@ function importApp(req, res, next) {
     });
 }
 
+function exportApp(req, res, next) {
+    assert.strictEqual(typeof req.body, 'object');
+    assert.strictEqual(typeof req.resource, 'object');
+
+    apps.exportApp(req.resource, {}, auditSource.fromRequest(req), function (error, result) {
+        if (error) return next(BoxError.toHttpError(error));
+
+        next(new HttpSuccess(202, { taskId: result.taskId }));
+    });
+}
+
 function clone(req, res, next) {
     assert.strictEqual(typeof req.body, 'object');
     assert.strictEqual(typeof req.resource, 'object');