Posts!

A bunch of changes to make more space on the homepage, and then a stream of posts in the space freed up.

- Calendar is now agenda display to make more room on the homepage (also IMO it's more readable).
- Summary boxes have been removed, because half of them were "nothing here", and to make more room
- Pub quiz and competition have lost their infoboxes because they're one-off.
- Weekly talks have acquired an (uninformative) infobox

We now have a stream of posts (in an entirely coventional Jekyll way). These will display the first paragraph as a preview, and paginate after 3 posts.

There is also now a file `_local_config.yml` to give to `jekyll serve`, as there seems to be no sensible way of overriding jekyll's `url` parameter on the command line.