Multiple forecast areas and improved forecast archive

[kellpossible]

With there being a chance we will produce a Svaneti forecast this season, it seems prudent to get ahead and build support for multiple forecast regions on the website. This will involve the following changes:

• Redesign of the home page to show the different regions, and a summary of the latest forecast.
• A page per forecast region which displays the latest forecast along with a link to the forecast archive for that region.
• In order to show the latest forecast (and forecast archive with the avalanche danger) efficiently we probably want to cache the parsed forecast json in the database.