[4.0] Added automatic premultiplication of image visual images

[4.0] Added automatic premultiplication of image visual images

To prevent scaling quality issues, image visual images are pre-multiplied after loading.
By default, this is on, but it can be turned off via a new API in VisualFactory.

Conflicts:
	automated-tests/src/dali-toolkit-internal/dali-toolkit-test-utils/dummy-visual.cpp
	automated-tests/src/dali-toolkit-internal/utc-Dali-TextureManager.cpp
	automated-tests/src/dali-toolkit/utc-Dali-ImageVisual.cpp
	dali-toolkit/devel-api/visual-factory/visual-factory.h
	dali-toolkit/internal/visuals/animated-image/fixed-image-cache.cpp
	dali-toolkit/internal/visuals/animated-image/rolling-gif-image-cache.cpp
	dali-toolkit/internal/visuals/animated-image/rolling-image-cache.cpp
	dali-toolkit/internal/visuals/image/image-visual.cpp
	dali-toolkit/internal/visuals/texture-manager-impl.cpp
	dali-toolkit/internal/visuals/texture-manager-impl.h
	dali-toolkit/internal/visuals/visual-factory-cache.h
	dali-toolkit/internal/visuals/visual-factory-impl.cpp
	dali-toolkit/internal/visuals/visual-factory-impl.h

Change-Id: Id1606e156f2d31d858bb4ddc65cbf97ed3efba5c
Signed-off-by: David Steele <david.steele@samsung.com>