clouds: new object that generates clouds in areas

- grove01 now starts with 5 clouds and generates a new one every 10-20
  seconds.
- When clouds go offscreen they are deleted.
testing: add clouds to all outdoor areas
cave01: clarify indentation
grove01: expand, re-layout

In several places, the viewport will not bump up against the edge of
the area anymore.

bump TsunagariC to 6f1c46b