Added tini to help xvfb-run work

Installing mesa utils for headless rendering.

Enabling procedural nodekit in Docker build

Added frame loop to osgearth_server to allow it to render layers that…

… use the TileRasterizer.

Change server listen address to allow external connections

Added experimental osgearth_server application.

Version 3.7.2

Tag osgEarth 3.7

tag version 3.7

Tag version 3.6.1