Player properties: Set correct default collisionbox

Player properties: Set correct default collisionbox

Recent commit b6f4a9c7e1a4f0bac66fd6f6ff844425ac775975 removed a hardcoded
player collisionbox which resulted on falling back to an incorrect default.
This stopped players walking through 2-node high spaces and made the player
slightly wider.

Improve docs for custom player collisionbox feature and reformat nearby lines.