add discard button to validation screen also

atdb/logs/atdb.log

...askdatabase/templates/taskdatabase/discarded/headers.html

.../taskdatabase/templates/taskdatabase/discarded/tasks.html

atdb/taskdatabase/templates/taskdatabase/failures/tasks.html

...se/templates/taskdatabase/validation/confirm_discard.html

...skdatabase/templates/taskdatabase/validation/headers.html

...taskdatabase/templates/taskdatabase/validation/tasks.html

atdb/taskdatabase/urls.py

atdb/taskdatabase/views.py