Make first write through of Danish documentation

[dybber]

• [x] Move epidemic tutorial from .tex to reStructuredText
• [x] Draft subpages and structure of the documentation
• [x] Translate introduction
• [x] Write "Get started" page
• [x] Test epidemic tutorial, and update with recent changes to model spec
• [x] Add images to epidemic tutorial

[JensKanstrupLarsen]

I think the last three points might be fixed in #102