Question List Mode implementation

This uses tabulated-list-mode to build the list of questions.
The actual content of questions is displayed on a separate buffer using org-mode (for now of course, this is not permanent).
The problem is that, in order to run inside `tabulated-list-revert-hook`, it needs to be able to work without arguments.

We could construct a lambda which gives it the data as arguments (and put *that* inside the `revert-hook`), but then this data would be static, and wouldn't update as the user reads questions and stuff.

I guess we could give an entire data structure (such as the one used for the question list), and then updates to this structure would be seen by the function.

Ok, I'll use a lambda for now.