feature/voronoi-container

[boygirl]

This PR supports FormidableLabs/victory-chart#432

This PR:

• Adds a theme prop to VictoryContainer so that custom containers may pick up themes from their parents
• Removes default title and desc props from VictoryContainer
• Adds support for providing text as an array for VictoryLabel
• Adds support for providing style as an array for VictoryLabel so that each line of a multi-line label may be styled independently
• Changes how null data values are handled by Area and Curve primitives
• Adds a reduceChildren method to Helpers to ensure order consistency when working with nested children
• VictoryTooltip no longer automatically adds the active prop to data when hovered. To turn this behavior on, set the new activateData boolean prop on VictoryTooltip