Final updates to M4->BETA1 migration process.

The update process was taking too long to delete candidate data
using the normal API, so I've split this into a single FS delete
and DB deletion (within the SQL migration script).

The SQL migration script has been renamed appropriately.

I have also added in logic to delete all LTI candidate users from
the system at this time, as they shouldn't be kept in the system
after having their candidate data removed.
Made "Quick Try" buttons in ass list more robust

They were wrapping oddly when testing on Sue's assessment list,
so I've replaced the space with a &#xa0;