Add history listing of deleted objects

[macro1]

It has been a really long time since I looked at this, and it turned out easier than I thought. Of course, the main admin page for the object will still give you a 404, but if you navigate directly to the history page you'll be able to view the list of changes after an object has been deleted.

resolves #72

[KevinGrahamFoster]

Very cool. Thanks!

[marcgibbons]

@macro1 Any thoughts on how best to access the list of deleted objects from the admin?

[macro1]

@marcgibbons: The change above was to allow the page listing all changes to an instance (all the entries in the history table) to be visible even after the object was deleted. We don't currently offer a way to find back deleted instances easily in the admin. (So the list of changes are available, but only if you know the id of the deleted instance already.)

As always, if you find this is something useful to you, feel free to make a pull request and we can see what it would take to get it offered as a feature. If you don't feel up to the task, you can open an issue as well, describing what you're looking for.

Edit: I think I can see where some confusion may have arisen. #72 requested a list of deleted instances as well as the ability to see those histories. I only accomplished the second part, so I reopened the original issue.