When no fields are defined we should not displayed 'Add entry' tab

1. Create a database a teacher (do not setup it up)
2. Connect as student, go to the database, and click on Add entry.
=> An error message is displayed.

imo we should not see add entry tab if we cannot add an entry. Otherwise if we keep this tab, the error message should not be an exception. And if we keep the exception (you really not like my suggestion ) the button continue should return on the course page, not the front page.

When there are no fields defined, all tabs should not be displayed and show the message 'No entries on database' instead.