A bunch of changes (Bootstrap css, numbering, accordion sorting, protoypes, status array, readme, screengrab)

All the MRs so far (an array of status, Bootstrap CSS rather than custom) plus: snippet numbering, re-ordered Accordions to match the Accordion issue, and three 'prototypes'.

I realise that's a bit of an extra feature for the extension - acting as sandbox for proposed new markup patterns - so I'm also OK if you don't merge this! But it seems as good a place as any. My thinking is prototypes could be reduced to the one accessible accordion we agree on, and once it is supported by Civi Core, it can become status 'recommended'..