Feat/study closing: Add option to close a study

[hig-dev]

This PR adds the feature to close a study. It is not possible to re-open a study. No new participants will be able to enroll in a closed study.

• [x] Database: Add "is_closed" column to study table
• [x] Database: Add policy to restrict joining a closed study
• [x] App: Do not show closed studies in study selection
• [x] App: Show dialog if user tries to join a closed study
• [x] Designer: Use study status to show state of study (running, draft, closed)
• [x] Designer: Adapt study duplicate function
• [x] Designer: Add feature to close study using modal actions
• [x] Designer: Add banner to recruit page for closed study