WebStyle: error code 401 on authorization failure

• Adds error code 401 when user is not authorized instead of just flashing an error message with a success code.

• Uses same unauthorized handler in Flask login_manager as 401 error handler.

• Fixes webstyle regression tests.

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Co-authored-by: Konstantinos Ntemagkos <konstantinos.ntemagkos@cern.ch>