New site configuration schema

[MortenHofft]

To allow more types of content we need to update the current format that looks like

// occurrence config only
siteConfig = {
  rootPredicate: ...
}

to something that allows more types as well as routing

{
  routes: {...},
  occurrence: {
    rootPredicate: ...
  },
  dataset: {},
  ...
}

Both theme and widgets and individual sites needs updating. I will do my best to coordinate the deployments it in such a way that there will be no outages.