UI updates

[PizieDust]

This PR does the following.

• Separates the layout into authenticated and guest layouts.
• Displays error messages in a dedicated UI (different for both authenticated users and guest users.
• A single module to manage responses.
• A page for user management (on the dashboard sidebar menu Users)
• Adds cookie authentication to the configurations endpoint. (Login and Register I believe don't require the user to already be authenticated so these are open).

[hannesm]

This looks nice. Just for my understanding:

• when /api/YYY is requested and an error occurs, a json error is being sent back
• when another page is requested and an error occurs, the error page is displayed

both use the HTTP reply code that is the error code as well!?

[hannesm]

thanks a lot!

[PizieDust]

This looks nice. Just for my understanding:

• when /api/YYY is requested and an error occurs, a json error is being sent back
• when another page is requested and an error occurs, the error page is displayed

both use the HTTP reply code that is the error code as well!?

Yes exactly. This is the idea.