Exception for different `VIEW_PROJECT` settings of default map

Case (anonymous): VIEW_PROJECT == 1, testuser: VIEW_PROJECT == 0:

Clicking on the lock symbol and logging in as testuser leads to a tomcat exception shown in the web interface:

HTTP Status 500 - User doesn't have access to project
type Exception report

message User doesn't have access to project

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: User doesn't have access to project
	javax.faces.webapp.FacesServlet.service(FacesServlet.java:606)
	org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:98)
[...]

Proposed solution:

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.

Bug originally was a part of #251 (closed)