Add StartValue Override to Storyboard Animations

[menvae]

This would make complex animations in storyboard much easier.

Changes

• made use start value false by default when adding new animations
• add start value to storyboard animations
• made start value nullable for lua animate method, making it nil will not use the start value
• minor refactor to everything that uses startValue

[flustix]

Missing JSON attributes in some places.