Verify all assumptions in a system are used in some way

[balacij]

It would be nice if we could check whether every assumption is used somewhere. If an assumption is in the list of assumptions, then somewhere else in the document we should "invoke" that assumption to do something.

We already make sure that every symbol in the table of symbols is used in the document, since the table of symbols is constructed from the chunks. I like that example, but I can't think of anywhere we can mention it in the paper, without having to give too much background information and putting us over the page limit.

Originally posted by @smiths in https://github.com/JacquesCarette/Drasil/commit/3146ee1777edeaf0cb4f758a6efc181c696f1dde#r58074750

[balacij]

I believe that with #2873, this should be very easy to do (and is a good example of what a "system requirement" could be as per #2883). We can do this by chunk "reference analysis".

[smiths]

Sounds good!