- Linked polls migrations
- Batch polls import from yml (shown for linked_polls elections)
- Redirect voters to linked polls after each vote cast
- Display linked poll links in voters election view
- Linked polls exclude voter handling
- Send only one vote/info email for linked polls (new template used for
  body)
- TODO: include audit codes for all polls, separately
- Display 'linked' notification in polls list
- Include migrations for new fields
- Do not display poll.name in election view if poll is linked