Simpler form factor code

This branch only tests for modern Android and iOS form factors.  The regex is much simpler to understand, although it'll probably miss a couple of devices that the code in the moreua branch won't.

When I have time I'm going to create a separate project that only deals with form factor, and GWTP can then either depend on that, or I'll add a module so that people needing more accurate form factor can easily override GWTP's form factor code.