Animated Gradient Visual in devel-api

Animated gradient visual. Can be used for Control's background.

At Internal::AnimatedGradientVisual :
 - Use only one shader codes to draw effects.
    *NOTE : We change shader string at AnimatedGradientVisual::CreateShader()
 - When DoSetProperties occured
   --> Set non-animated properties (for make Renderer)
   --> Set animated properties (for make Animations)
 - When DoSetOnStage occured
   --> Make Renderer
   --> Make Animations
   --> Play Animations
 - When DoSetOffStage occured
   --> Stop Animations

At AnimatedGradientVisual::Property :
 - 3 non-animated properties.
  - GRADIENT_TYPE = LINEAR / RADIAL
  - UNIT_TYPE = OBJECT_BOUNDING_BOX / USER_SPACE (See GradientVisual::units)
  - SPREAD_TYPE = REFLECT / REPEAT / CLAMP (See GradientVisual::spreadMethod)
 - 7 animated properties.
  - START_POSITION ( Vector2 )
  - START_COLOR ( Vector4 )
  - END_POSITION ( Vector2 )
  - END_COLOR ( Vector4 )
  - ROTATE_CENTER ( Vector2 )
  - ROTATE_AMOUNT ( Float )
  - OFFSET ( Float )
 - Every animate properties have there each values
  - START, TARGET, DIRECTION, DURATION, DELAY, REPEAT, REPEAT_DELAY, MOTION_TYPE, and EASING_TYPE.
  - animated by Dali::Animation::AnimateTo()
  - Setup properties by Property::Map

Change-Id: If85c08d4500d132b6d8de6ed016bf985770c846c
Signed-off-by: Eunki Hong <eunkiki.hong@samsung.com>