Token hiding

Wrap testVisibility in order to hide a token based on elevation.

Given one or more points of vision to a token:

• test for intersection with an Enhanced Terrain Layer polygon.
• Test if the token can be seen from the point(s) of vision, assuming 3-D elevation for the token, wall, and point(s) of vision.
• Hide token as necessary

Also adds a log debug flag using the devMode module, and currently sets a debug flag to visualize the terrain polygons and intersections.