MDL-14734 "improve interface for deleting attempts"

MDL-14734 "improve interface for deleting attempts"

* The control for deleting attempts is a drop down box with onchange javascript to submit the form, you cannot see the label to say what the drop down box does. Better to use a button. The button label is visible so you can see what it does.
* Checkboxes should be displayed when there is no attempt to delete.
* The whole column for checkboxes should be removed when no attempts are displayed ie. when showing students with no attempts.