Reduce the near clip distance

[pdavidc]

Modify World Wind Android to use the closest possible near clip distance that does not result in z-fighting. Currently, WWAndroid sets the near clip distance to 75% of the eye altitude, which is farther than necessary for the majority of eye distances.

World Wind Java implemented this capability by computing a near clip distance that achieved a 10 meter depth resolution at the far plane, a value empirically found to be sufficient for WWJ applications. See WWJ-460 for details:
http://issues.worldwind.arc.nasa.gov/jira/browse/WWJ-460