Add rugplot/segment plot for sgRNA rank.

[j-andrews7]

Condensed representation of sgRNA rank for a given gene, add vertical segment for each sgRNA in gray, highlight those for selected gene in red.

This could also be useful for highlighting specific genes/pathways in the gene rank plots.

[j-andrews7]

This should be added as a parameter to the plot_rank function, e.g. plot.density = TRUE. Under the rank plots, I just want the rug plot, as shown here. But we construct the rank plot directly in plotly whereas the examples only show how to make rugplots in ggplot2 and then convert to plotly via ggplotly.

There is almost certainly a way to do this natively with plotly, but I have not yet found it.

This should be FALSE by default and a checkbox added to the Rank Plot inputs to control this for CRISPRball.

[j-andrews7]

Worst case, can make the rugplot via ggplot2, convert via ggplotly, then add below the rank plot using subplot.