SequenceBoard: boxes misplacement

On linear sequence, the boxes can be misplaced if the column count is not equal to the # of sequence groups / line count: e.g. if there is 12 groups and the width of the screen is such that 5 columns can be displayed, there will be ceil(12/5) = 3 lines so the computed column count will be 12 / 3 = 4 ≠ 5, leading to a misplacement. This can be seen on guide GD_00001.