Clean up the appearance of the horizontal 'all regions' view of the Ideogram view

[carolinebridge]

Currently, showing all regions in an ideogram view isn't very concise with a horizontal orientation. All chromosomes are stacked on top of each other, creating a very tall view container.

A potential solution to this is to maintain two ideograms side-by-side showing the first and second half of the regions in the assembly, using the chromosomes: string[] property on the ideogram config.

Using the rows: number property on the ideogram config seems to cause visual issues, though this is another potential solution.

Another improvement to the visual when the ideogram is in horizontal view is to centre what is being displayed inside the view container.