Added support to recast a column (from Name->String or String->Name, basically).
Came up with a too-clever-by-half algorithm which converts one datatype to another by checking to see if there is specifically a constructor of the form ToClass(FromClass x). That -- and the standard case that any String can be created from any Object -- should keep us going for a while, I think.
Created a ColumnInformationPanel for displaying column-related information to the right of the screen.