BUG: Some duplicates ending up in responses object for checkbox questions

[freemvmt]

Only seems to happen when other submission is included (navigate away and back to see this).

Check reducer functionality for this case.

[freemvmt]

Fix: swapped 1st and 2nd branches in checkbox branch of reducer (hadn't anticipated that the re-selection of checkboxes other than the 'Other' option would also be non-trusted events i.e. programmatically rather than user generated)