Add randomness to bump distances

[rachel-fenichel]

Problem statement

Blocks bump fully deterministically. A block that has just been bumped does not bump blocks from its new position, to avoid cascades. As a result, bumped blocks can end up stacked on top of each other and can be hard to read.

Expected Behavior

Block bumping improves readability and stops blocks from being stacked in misleading ways.

Actual Behavior

Additional Information

Proposed solution: add some randomness to the calculation for how far to bump a block. Probably +/- 5 or 10 on both X and Y. That change would be here.