Basic seed-based object container placement

[benwiley4000]

This will be a prerequisite for proper rendering of procedurally generated objects in the world.

• [x] Given the world position of a WorldTile as input, produce a predictable set of 2d boxes for trees and rocks to occupy
  • [x] Trees will be square-based, so same x and z spans
• [x] Create placeholder classes for Tree and Rock
  • [x] Each renders a 3D GL_LINES container (of arbitrary height) in the space a tree or rock would occupy
  • [x] Class constructors should take the following inputs:
  • world x position
  • world z position
  • x span (same as z span for tree)
  • y span (rock only)