This will allow for the facing direction of each node to be easily
determined without being able to see the top side.

The detector's top side texture has also been notably rounded compared
to the node creator.

This is a usability feature to aid box builders with various
colorblindness issues.  The symbols may also aid new builders
in memorization of node functionality.  Additionally, directional
indicators were added to the sides of Node Detector and Node Creator
nodes, to make it clear which direction they're pointing when the
top is not visible.