…with displayXAccessor instead of xAccessor, as MouseCoordinateX does (for discontinuousTimeScale, xAccessor will give index, not date)

1. devicePixelRatio / backingStorePixelRatio for correct image scaling on Retina devices
2. use file-saver for correct image saving on IE/Edge/Safari
3. add canvg parameter for fallback when saving in IE11/Edge (IE has security bug when trying to save canvas with any svg image painted on). See https://developer.microsoft.com/en-us/microsoft-edge/platform/issues/1015651/ or similar bugreports. See description for canvg parameter here: https://github.com/exupero/saveSvgAsPng (canvg - If canvg is passed in, it will be used to write svg to canvas. This will allow support for Internet Explorer)
4. Add paddings parameter to save functions