[x] Enable locking of cells, rows, columns to prevent editing once dataframe is built (currently implemented, but disabled for debugging).
[ ] Instead of creating columns on the fly, implement a buildColumns method to generate them all at once (will also be useful for creating split versions of DataFrames, when rows are split to the left or right at a tree node).
buildColumns
method to generate them all at once (will also be useful for creating split versions of DataFrames, when rows are split to the left or right at a tree node).