Renew our wordpress theme

[harry-wood]

We're based on a an old theme, "twentytwelve" which dates from ... 2012. There's probably some upstream maintenance we might try to merge in, or we might simply re-do our theme based off something newer. Either way I suspect the weird issues like #10 may go away if we update things.

Also with the design I originally tried to mimic the look of the diaries, but then they changed a bit, so re-doing that whole thing wouldn't be such a bad idea.

I can volunteer to do this work (again) if you like, or if someone else is keen.

(I originally said this here: #4 (comment) but it deserves its own issue)