Range attributes

[johannesodland]

Adds support for getting and setting rangeStart and rangeEnd on Animation.

• Adds support for the 'normal' value
• Adds getters and setters for rangeStart and rangeEnd
  • setters are limited to ViewTimelines for now, as the existing implementation is limited to ViewTimelines
• Uses CSSNumericValue.parse() to parse string values for range start and range end.
  • This adds support for math functions such as calc(100% - 20px).