Introduce a new view prop for vertical tracks

[flekschas]

I wonder if we could introduce a new view prop called orientation to add support for vertical tracks.

This prop could either expect the following values:

• horizontal
• vertical
• 45deg

The degree option is probably less important

[sehilyi]

I like the idea. I will add a dedicated type (i.e., orientation: 'horizontal' | 'vertical') when supporting vertical tracks (#54).

[sehilyi]

My initial thought when design Gosling was to let users map genomic coordinates with a y channel (e.g., y: { field: "position", type: "genomic" }) to make vertical tracks, but I think your orientation idea is better because users can easily change the orientation by using the view prop (for band connection, for example, users are using four genomic channels x, xe, x1, x1e, and changing them to y, ye, y1, y1e will be cumbersome.)

Perhaps, we need to rename x and y when using the orientation idea since x and y axes are determined by the orientation prop (currently, in vertical orientation x will be actually mapped to y-axis).