This thing is so cool and only recently I found about it. You can create pseudo fields with your entites, most often content types. So you can make some add, edit, delete buttons or any kind of forms on your entites or nodes. And it is pretty quick and straight fwd solution.
Read more about it here
https://www.computerminds.co.uk/drupal-code/add-stuff-node-and-configur…
http://www.vdmi.nl/blog/attach-extra-or-pseudo-fields-any-entity-drupal
or to have a real life working code with form and starting point, download commerce_backoffice_order.module and in that file you will find pseudo code for adding a dropdown for changing drupal commerce order status. I made a fork out of it and it was very fast, I made a Approve button for orders (just a form that makes order change status to approved) in minutes.