Reduce number of columns in grid_dropdown if user changes selection
	modified:   app/controllers/questions_controller.rb - if column count is
	greater than the number of columns requested, ask question_group to delete some
	columns

	modified:   lib/assets/javascripts/surveyor_gui/surveyor_gui.js - Make sure to pass
	a null index (NaN) rather than 0 if the user has not yet asked for a specific number
	of columns.

	modified:   lib/surveyor_gui/models/question_group_methods.rb - add trim_columns method
	to get rid of excess (more than the user wants) columns.