Move meta description and page class to base layout #230
When adding formats it's easy to forget to set the meta description to the content item’s description. This is a sensible default. Description isn't always present (eg html publications), in those cases omit the meta tag.
Almost all formats set the page class consistently to the dasherized version of the format name. Make those that were slightly different consistent and switch responsibility to the base layout, DRYing up the format templates. This reduces the risk of a format being accidentally added with a different page_class behaviour.
* Simplify each of the formats * Protect against formats forgetting to include