Added a columnSelector display option 

Added an option to griddly bear, columnSelector. If it's true, a button will be added to the footer that displays a dialog with a checkbox list of all the table columns hidden or not. You can then select which ones to display. If there's a column that doesn't have a title property defined, the checkbox list will use the column.id field as an identifier, but the table heading will be a non-breaking space.