Updated for new gov.uk website

Hey!

I've made a bunch of changes to get your DSACancellationChecker to get it working with the new gov.uk website, and thought I'd let you know so you could keep it up to date.

Comparing the code, the new website seems a fair bit simpler than the previous one, and hopefully should be easier to maintain as the HTML is all fairly well structured.

I've also made a couple of minor changes to tweak dependencies, add platform independent mail-sending so Windows users can use the script too.

Thanks for the hard work creating the original version - it was very handy to have something to start off from.