add orientation option to beeswarm (like in quasirandom)

[AaronRendahl]

With the new code that automatically chooses the direction to group on, groupOnX was deprecated, however, there are still some use cases for which the direction is not chosen properly. quasirandom has a new "orientation" option to allow the user to fix this, and beeswarm should have it too.

My particular use case is for logistic regression, where I like to plot both the points and the fitted line. To plot the fitted line, one must use 0/1 as the response, however, then both axes have numeric variables and the choosing code picks the horizontal axis, not the vertical axis.