Add ability to order Signal Columns

[timgaunt]

Sometimes when triaging an issue we select the Columns in the wrong order i.e. CountryCode > JobName > CountryId but you'd find it more useful if it was JobName > CountryCode > CountryId -without removing them and re-adding them in order there's no way to change the order

It would be really helpful if you could drag/drop the order of the columns in the GUI without having to edit the JSON