Resolve "Header icons on unauthenticated pages" (1)

Closes #27 (closed)

What does this MR do (summary)?

Adds the proper icons on pages that can be accessed when unauthenticated.

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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.