Enable user's to open the ballot at a later date

[karynemayer]

Overview

We want to enable the user to open the ballot at a later date. For that, we need to enable the checkbox in the ballot creation and create a button for open the ballot.

Acceptance criteria

• User can select to either immediately open the ballot or do it at a later date
• Immediately opened ballots should be immediately opened
• Ballots opened later should show a 'Start voting' to their creator only
• The preview components should reflect that the ballot is not open for voting.

Technical considerations

Tasks

• Enable the open at a later date checkbox in the create poll form
• Create the button that opens the selected ballot
• Ballot filters do not show non-started ballots #218
• BallotView should support DCMS-v2 and not-opened ballots #206
• BallotListItem should support DCMS-v2 and not-opened ballots #205