Cleanup db

[Katrix]

• [ ] Add message table
• [ ] Add nullable message_id column to logged_actions
• [ ] Replace message stuff in notifications with message_id column
• [x] Remove name in organization
• [ ] Replace comment in flags with message_id
• [ ] Replace message in project_log_entries with message_id
• [x] Merge project_log_entries and project_log
• [ ] Replace comment in project_version_reviews with message_id
• [x] Remove assets from project_versions. It's unused.
• [x] Remove owner_name on projects.
• [ ] Replace notes on project with associative table between project and message_id.
• [x] Replace username in user_session with user_id
• [ ] Run cleanup triggers a bit less often (every night)?
• [x] Create a materialized view for the front page which is updated every x hours