Hart candidate

Have addressed a number of issues from FixMyStreet-Commercial#476 and rewritten/squashed things to be clearer.  I can obviously carry on making minor tweaks, and/or attempt more ruthless rewriting of history, but would appreciate guidance on that if it's required!

I've ticked all the items I've made *some* progress on (some of them, like the "how much of Bromley was reverted" are partial -- I think there's a case of diminishing returns here, but I've certainly removed some of the confusing to-ing and fro-ing.)

I'm not sure why we needed the negative margins, it may be because of a bad CSS decision elsewhere.  Will ask Steve/Ben for suggestions on improving that.