Refs #9043 Added button and widened choose columns

The main gui now has a button that launches the choose columns dialog.

Choose columns now responds to Ctrl-M

The choose columns dialog has been widened, hopefully this should look better on mac now.
Refs #9043 Fixed some comparisons to improve robustness

I believe that the problem that owen mentioned was due to some of my column checking comparisons, so i've fixed them to save out of bounds errors as well as makign it more robust against unforseen problems.