Added support for elevation chunks in the Component interface.  Added a helper for handing elevation data to existing tile sources.  Put together a test mode for elevation in the tester app.
Fixed a problem with skirts in elevation mode.  Fixed a problem with lower res fill in tiles in elevation mode.
Merge branch 'refs/heads/wg_base/develop' into develop

Conflicts:
	WhirlyGlobeSrc/WhirlyGlobeComponentTester/WhirlyGlobeComponentTester/TestViewController.h
	WhirlyGlobeSrc/WhirlyGlobeLib/include/ElevationChunk.h
	WhirlyGlobeSrc/WhirlyGlobeLib/src/MBTileQuadSource.mm
	WhirlyGlobeSrc/WhirlyGlobeLib/src/TileQuadLoader.mm
Updates to terrain test