Fix elevation processing issues duning rendering

[EMaksymenko]

Description of the Change

• Added globe.getElevationAtLocation() method to determine real (not-tessellated) elevation at specified location.
• Fixed GL near clip distance calculation and limit Navigator to avoid camera below terrain.
• Fixed lookAt position calculation for gestures to rotate around point on terrain (not at zero altitude point).
• Add Elevation value output into exabple application.
• Tests which uses Navigator were commented as it is now dependent on Android context.

Why Should This Be In Core?

There was a terrain tessellation implemented in previous release, but it has been not involved in camera clip distance calculation and gestures processing. As the result camera is now rotating around the point below the surface and may render below the surface which cause graphical artifacts.

Benefits

Correct behavior of camera respecting terrain elevation.

Potential Drawbacks

None