candleStick, ganttChart, lineChart chart and components improve init() date domain calculation

[jamesleesaunders]

Assess whether it is appropriate to use the dataTransform module to also calculate 'date' and 'high/low' domain/extents. Refactor dateDomain and candleMinMax code found in:

• chart.candlestickChart()
• chart.lineChart()
• chart.ganttChart()
• component.lineChart()
• component.candleSticks()

Also consider which data format should be used as d3-ez's standard date format (i.e Unixtime or Date());

[jamesleesaunders]

See: https://github.com/jamesleesaunders/d3-ez/blob/master/src/chart/candlestickChart.js#L62 https://github.com/jamesleesaunders/d3-ez/blob/master/src/chart/candlestickChart.js#L76 https://github.com/jamesleesaunders/d3-ez/blob/master/src/chart/lineChart.js#L75