Fix namespace. It is <gx:duration>.
flyTo as a tour primitive
Attach flyTo to playlist
Fix flyTo writing
Template based convenience method to omit writing default values
Register properly. Don't write default values.
Attach abstract view children to fly to as well
Fix name (copy/paste error). Don't cast.
Write camera / lookat tags in flyto
Generalize abstract view writing.
Save home vs current location button state. Sanitize ctor.
Marble widget can be null
Don't complain when loading a Tour
Add support for the gx:Wait KML element

GCI task #5819304473788416
REVIEW: 114281
introduce MarbleView
introduce MarbleGLView
introcude GlLayerInterface
clear depth buffer between layer rendering
TextureLayer
PlacemarkLayer