Add option to lock log-ratio axis

[gibsramen]

One thing I noticed when playing around with feature balances is that the auto-scaling y-axis can sometimes mask the effect size of log-ratio differences. For example, a balance with more outliers may "squish" the boxplots closer together even though the difference may, in fact, be larger than between the previous set of boxplots.

(Will attach a screenshot later.)

I think adding an option for the user to "lock" the log-ratio axis might make it easier to compare between different numerator/denominator feature sets.

[fedarko]

This is a solid idea, and I think it should be pretty feasible by manipulating the Vega/JS stuff. Do you imagine adding a button/checkbox/etc. that locks the y-axis to the currently shown range, or adding stuff that allows the user to explicitly set the y-axis range? (e.g. two text boxes, one for the bottom y-value and one for the top y-value.)

edit: so this should be possible (in a somewhat limited sense) by making the zero parameter of the y-axis scale configurable. In #218 we changed this to always be false (so 0 isn't mandated to show up in the plot), but if we make this configurable via e.g. a checkbox that would work well (and it'd be easy for people to use).

[gibsramen]

Personally I would prefer the latter option to set values.