Availability of Applicability testcases

Most of the existing [test cases](https://github.com/buildingSMART/IDS/tree/master/Documentation/testcases) (which are really useful BTW) seem to exercise the Requirements scenarios over the Applicability side of things.

I'm presuming that's since Requirements are the primary focus of the specification, but it would be good to have some reference cases for Applicability so all implementors have the same understanding.

Following on from #177 a few queries I had:

* Presumably any of the 6 facet types can be used for applicability? Each of the markdown docs has a 'Applicability Intention' section that indicates this is the case
* When facets are combined, are we expecting the intersection of the results or the union? (Assumption is it's the Intersection)
* Is sequencing of facets important?
* Can minOccurs/maxOccurs (cardinality) be applied? What does Required, Prohibited and Optional mean in the context of an Applicability facet?
* Can a facet be used more than once? E.g. To find all External elements with a FireRating would be two Property facets.
* What is the expected behaviour with no applicable matches?

Feels like it's worth getting clarity on these if we've not done so already.