Multiple forecast areas and improved forecast archive

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.
- [x] 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.

No files, tests, or entry points are named. Start by locating the existing home page, forecast display and archive handling, then trace how parsed forecast JSON is stored in the database. Done means the site supports multiple regions, each with a latest forecast and regional archive, while using the planned cached data.

Written by the indexing model from the issue text.