Add additional tick marks for y-axis of intersection sizes

[janstrauss1]

Hi @JakeConway,

Thanks for your efforts to develop UpSetR!

I am currently trying to polish off a figure for a publication and I would like to add additional tick marks (add major tick marks and specify minor tick marks) to the y-axis (Intersection Size) of my UpSetR plot. Current tick marks are at 500, 1000 and 1500.

This somewhat relates to the closed issue #43 but I couldn't find an answer there but only how to control font sizes of the tick mark labels. E.g., is there a way to return a data.frame from the upset function (like the returnData argument from plotting functions in DESeq2 for customized plotting with ggplot?

Many thanks in advance for your help!