UIShiny : Visual update

[mob-sakai]

Merge from ShinyEffectForUGUI v0.4.0

• Use 'brightness' instead of 'alpha'
• Improve Visual quality
• Width of the effect should be ranged [0-1], not [0-2]
• Add softness parameter
• graphic.color.a decrease the brightness of shiny effect
• Improve precision of location parameter