Env dof controller

This entity controls the depth of field settings for all players. This can be used to simulate a human eye's focusing abilities.

This entity's variables are a little confusing, so a quick explanation follows in the order that they apply:
 * Near Blur Radius: How much to blur objects when they're too close to the viewer.
 * Near Blur Depth: Objects closer than this distance to the viewer are blurred by the Near Blur Radius. Objects beyond this distance will be less and less blurry as they get closer to the Near Focus Depth.
 * Near Focus Depth: Objects past this distance are in perfect focus. They will stay in perfect focus until they reach the Far Focus Depth.
 * Far Blur Radius: How much to blur objects when they're too far away from the viewer to see clearly.
 * Far Focus Depth: Objects beyond this distance will begin to get blurry as they get closer to the Far Blur Depth.
 * Far Blur Depth: Objects farther than this distance from the viewer will be blurred by the amount specified by Far Blur Radius.