title: Add new entities in OpenCart
body: <p>I was wondering if I can add new entities (classes/tables) in OpenCart to store information that is not included in the default functionality. To be more precise, I would like to add subscription (3/6/12 months) related information, as described here:   <a href="https://stackoverflow.com/questions/11244247/opencart-subscription-model-x-months">OpenCart subscription model (x months)</a></p>
  
  <p>If yes, can I just add admin pages for the new class? Would something like: <a href="https://stackoverflow.com/questions/10700761/how-to-create-a-custom-admin-page-in-opencart">How to create a custom admin page in opencart?</a> work?</p>