Feature: Display row and column counts before/after each pipeline stage

[pebenbow]

Would be great to show a count of rows and/or count of columns before AND after each stage of the pipeline. This will give users a better sense of the impact of their transformations.

This also applies to joins: how many rows and columns are contained in the resulting data frame?

[pebenbow]

Another suggestion: show row counts by default on the detailed view, but hide them by default on simplified view. Give users an argument that allows them to always hide these.