Autoelevation, Enhanced Terrain Layer, and 3d Canvas fixes
Refactor token elevation calculator class. Now split into three parts:
- CoordinateElevationCalculator: Elevation using a single point.
- TokenPointElevationCalculator: Simple wrapper on (1) to accept a token instead of a point. Measured by token center.
- TokenAverageElevationCalculator: Extends (2) to use averaging over token shape.
This provides additional tools for Elevation Ruler.
Add automatic elevation support for Enhanced Terrain Layer.
Better support for 3d Canvas.