Create a preview mode for publishing survey data

• The compendium frontend now has a preview flag that can be activated by visiting any data page with a ?preview query parameter. This works with the usePreview hook that uses the previewContext
• This preview flag is passed along to the backend (again as ?preview ) in all api calls in the new useData hook
• We have a new preview_year table that contains the years that should only be visible in preview mode
• This table is used in the new get_data helper function that is called from all the routes
• The preview_year table is managed from the survey management page, that now has a 'preview' and a 'publish' button (there's a corresponding new endpoint for the preview button)
• To keep track of whether the survey is in preview there's a new 'preview' survey status. The 'checked' response status is removed because it isnt used