Make backto parameter consistent on mod/data/edit.php

The workflow should be as consistent as possible for users, so we could improve the backto parameter to:

• When the user navigates to edit an entry from the single view template, cancelling the edition should redirect the user to single view template.
• When the user navigates to edit an entry from the list view template, cancelling the edition should redirect the user to list view template with the right pagination.