Redesign

What does this MR do (summary)?

• Implements the redesign for every page.
• Removes unused endpoints.
• Adds more specific methods to the AuthorizationService.
• Implements (read: "steals from Queue") caching to minimise the amount of requests per page.

Does this MR meet the acceptance criteria?

• The main application was run to make sure the server still runs without errors.
• Tests were written to verify the behaviour of this code.
• Javadoc and other comments were added to make the code understandable.
• The code adheres to the style guidelines.