Implement zooming in PheWAS plot

In many cases, Open Targets Genetics reports one association for a variant that is vastly stronger than the others. As a result, this one dominates the scale of the plot, and it is difficult to see whether other associations are above or below the significance threshold. Indeed, their labels often overlap because of this, so it is unreadable.
Here are two examples:
1_154453788_C_T (the example on our homepage)