Handled modifications of the Color field in the ElevationGrid#fieldChanged method
Added copyright notice.
Added comments.
Merge pull request #394 from girier-tsha/elevation_grid_color_changed

Elevation grid color changed
Removed calls to invalidateVolume, unnecessary for mere color change.
Merge pull request #395 from girier-tsha/elevation_grid_color_changed

Removed calls to invalidateVolume, unnecessary for mere color change.
added missing physics lib to package and fixed corresponding issues