[Delivers #43492849] Allow management of repositories

I've introduced a repositories listing and edit workflow.

Repositories are no longer created via a dialog and now follow the same workflow as other records - "Create Repository" in the user menu has been replaced with "Manage Repositories".

As repo_code can now be edited, instead of storing the repository's repo_code in the frontend session, we store the repository's URI - this required a few changes to display labels and the introduction of the helper method current_repo.

In the frontend I also renamed the repository_controller and view folder to "repositories" to follow the plural-naming-convention.