During documentation of the pair programming feature, we noticed that the Contributor should be an abstract class, which is parent for the User and the ProgrammingGroup. With this commit, we perform these changes.
Since both projects are developed together and by the same team, we also want to have the same code structure and utility methods available in both projects. Therefore, this commit changes many files, but without a functional change.
By switching the `intervalstyle`, we assume to fix CODEOCEAN-FT. It is caused by by PgBouncer providing different database connections to Rails that might behave differently.
