[VisCanvas] axes and grid props

[axelboc]

Since extracting the logic out of VisCanvas does not seem practical (cf. #1276), here is an API proposal to at least:

• separate out the cosmetic options from abscissaConfig and ordinateConfig (i.e. showGrid and label);
• allow more control and extensibility than showAxes.

<VisCanvas /> // no axes, no grid
<VisCanvas axes grid /> // left/bottom axes + vertical/horizontal grid
<VisCanvas axes={{ left: true } }} grid={{ horizontal: true }} /> // left axis + horizontal grid
<VisCanvas axes={{ left: "Energy" } }} /> // left axis with label
<VisCanvas axes={{ left: { label: "Energy" } } }} /> // same but via options object for future extensibility (e.g. `showAxisLine: false`)

// and in the future, perhaps:
<VisCanvas axes={{ top: true }} />
<VisCanvas axes={{ left: true, right: true }} /> // with the same ticks and tick labels (since they'd be sharing the same ordinate scale)

I considered an opt-out API instead, where the left/bottom axes and the grid would be rendered by default and would have to be turned off, but it felt too cumbersome. I prefer an opt-in API with concise prop names and convenient shorthands.