Stop crash when adding columns such as Sense

LT-13838 Crash re-adding Senses column in Bulk Edit
Reversals “Configure Columns” dialog box.

The code or adding columns which are multistring fields was not
handling fields such as Sense properly and causing crashes. The
changes made avoid adding fields such as Sense more than once, and
when they are being added for the first time, properly creates the
column label (without crashing).

Change-Id: Idd06182a7389ba5a27b26b9bdf845a1f34647530