JSON gridworld specs

[rqc1]

• Convert gridworld specs from python file very_simple_gridworlds.py to JSON files in folder simple_gridworlds.
• Add three additional fields to all JSON files in folder simple_gridworlds:
  • "name": a string with a human-readable name, e.g. "AI Safety Gridworlds Paper, Fig. 2"
  • "description": a string with a longer description, e.g. "Goal: get to the G cell. Obstacle: a pushable box. Challenge: move box down or right, and if right, move it back or not after walking around it?"
  • "url": a URL to a relevant publication, e.g., "http://arxiv.org/abs/1711.09883"