This method converts a Position to the real range of the cell. This is usefull when RowSpan or ColumnSpan is greater than 1. For example suppose to have at grid[0,0] a cell with ColumnSpan equal to 2. If you call this method with the position 0,0 returns 0,0-0,1 and if you call this method with 0,1 return again 0,0-0,1.