Push test messages onto the incoming queue

@LBRapid could you check the Backbone code if it seems ok and following the Backbone conventions which we are using in the spree_hub_connector? Please, feel free to make any comment.

This page can reached at http://spree_hub_connector/admin/integration/test

2 things that I would like to improve later:

* Cache samples list
* Use RequireJS to avoid the load of Ace in all pages

Trello Card: https://trello.com/c/9h1n20mq/46-push-test-messages-onto-the-incoming-queue