Improved colour-legend display and labels

[andy-lee-eng]

Use a "nice" number range for display purpose only (doesn't affect the actual colours used).
Give the colour legend a bit more height, but less width, which it doesn't need.

Prevents legends from different charts interfering with each other.
Stores pageIndex in settings to preserve page position.

[Ro4052]

I'm still not 100% clear on how the legends were interfering with each other.

Other than that, looks good to me!

[andy-lee-eng]

@Ro4052 previously scrollColorLegend and scrollSymbolLegend were global instances of components that were re-used (to preserve pageIndex). However, that meant they were also re-used across multiple charts on the same page, which was not the intent.

Now, scrollColorLegend and scrollSymbolLegend are functions that return new instances of components each time, and the pageIndex is preserved by putting it in settings.