added clone functionality to Overlays:
Overlays.cloneOverlay(OverlayID)
filled in the rest of the properties
Merge branch 'master' of https://github.com/worklist/hifi into 20176
Added cloning methods to Grid3DOverlay
Added example script for cloning overlays (TODO: SpriteBillboard fix cloning of in example)
Fixed Overlays::isLoaded which did not to find my just created overlay.
added OverlayPreloader and made a bunch of clones
fix Ubuntu build
fix ubuntu build
Merge branch 'master' of https://github.com/worklist/hifi into 20176

Conflicts:
	interface/src/ui/overlays/Grid3DOverlay.cpp
	interface/src/ui/overlays/ImageOverlay.cpp
	interface/src/ui/overlays/Line3DOverlay.cpp
	interface/src/ui/overlays/LocalVoxelsOverlay.cpp
	interface/src/ui/overlays/LocalVoxelsOverlay.h
	interface/src/ui/overlays/Overlay.h
	interface/src/ui/overlays/Overlay2D.cpp
	interface/src/ui/overlays/Text3DOverlay.cpp
	interface/src/ui/overlays/TextOverlay.cpp
	interface/src/ui/overlays/TextOverlay.h
moved writeToClone to copy constructor
Merge branch 'master' of https://github.com/worklist/hifi into 20176
added const to copy constructors
Merge pull request #3794 from thoys/20176

CR for Job #20176 - Ability to clone Overlay in Javascript