Misleading messages for different `VIEW_PROJECT` settings of default map

Case (anonymous): VIEW_PROJECT == 0, testuser: VIEW_PROJECT == 0:

Opening the main MINERVA page leads to a popup

ERROR
Access denied.
Please login to access this resource

After clicking the login button and entering valid credentials for the test user, we are again shown Access denied. Please login to access this resource.

This is misleading, as we already logged in.

Proposed solution:

• If anonymous does not have the VIEW_PROJECT privilege, show directly the login page (not an error message).
• If a user is logged in but does not have VIEW_PROJECT privileges, show an error message like the following: Access denied. Please login as a different user or ask your administrator to change the permissions to access this resource.

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Bug originally contained more problems and was split into two (another part can be found in #256 (closed))