Deeplinking to pages in documents

[joepio]

Clicking on a search result should open the right page.

• Switch to nested model - each page will become a new document in the back-end. These have new identifiers, but they are not exposed. Add a pages attribute.
• The ResultCard components need to have various links, each to a page. Each page will be a nested object in a single hit. The Document component should map over these hits with some logic,
• The URL should be aware the selected page. (move component state to query param)
• We should set up a new parallel set of indexes to prevent breaking changes for existing users. The already indexed data should be remapped to the nested structure.
• Notify other ORI users of this new field.

[joepio]

Relates to openstate/open-raadsinformatie#287