Add snap to grid on horizontal blocks and vertical size

[grassick]

Blue vertical line should snap to grid, as should vertical resizing of widgets.

For horiz blocks, is currently done with weighting system, defaulting to 1 for each block. Could continue, but with constraint that all weights must total to N where N is the number of blocks, and further, that each weight * 60 / N is an integer.

Vertical size is actually controlling aspect ratio. Could snap to nearest 1/12th?