VictoryCandlestick label improvements

[boygirl]

Currently VictoryCandlestick only renders one label per candle. Instead, VictoryCandlestick should render labels for high, low, close and open (and maybe keep label?) Each label should be able to be styled independently.

Proposed prop additions:

lowLabels: the label accessor function for the low label
lowLabelComponent: the component to render for the low label
highLabels
highLabelComponent openLabels openLabelComponent closeLabels closeLabelComponent labels: (existing prop) will now refer to a label rendered near the center of the candle labelComponent`: (existing prop) will now refer to a label rendered near the center of the candle

style: this prop should change to include namespaces for lowLabels, highLabels, openLabels and closeLabels. Styles suppled to the existing labels style namespace should be merged with other label styles so that users can easily define a single set of styles for all the different labels types, and override individual attributes as desired.

Label placement should have nice automatic default behavior for horizontal and vertical candle orientations