add fields to variables

Adds four fields to the variables table.  
Almost every other edit page on the site has the input box label above rather than to the left of the box.  Is there some reason you did things differently here?  While I can understand your wanting to optimize screen real estate, there's also something to be said for a consistent look and feel to the site as a whole.

If you _are_ going to put labels to the left of their corresponding input box, leave some space between them.  There may be an existing CSS class ready-made for this; if not, invent a sensible one and apply it to all of these cases.  (The traits edit page also has a few cases where the labels are to the left of the input; you could fix the spacing problem with these at the same time.)