Archive changes and other fixes

The archive page will show tumblr-style thumbnails if a yearly archive
has been requested. If the complete archive is requested, a list of
titles only will be displayed to avoid a massive content payload.

The sidebar link to the archive now links to the most recent yearly
archive.

Fixed a snafu in the order of clean -> dirty URL translations that
meant the `url()` constructor could not build URLs for daily archives.
Also added a URL translation for yearly archives.

Fixed some missed translations, tidied some ugly Twig code for post
fields (refactored code plays nicely with syntax-highlighting in text
editors) and generated fresh .pot files.