Better support RMarkdown notebook's interactive paged tables

[michaelquinn32]

This is part of #667.

Some issues that stand out:

• All output panes are called one_skim_df
• Summary is referred to as "R console"; it doesn't render as a nice html table
• Html headings that we add are dropped

[llnelson]

And a related suggestion: allow skimr-generated histograms in HTML output to render correctly.

[elinw]

@llnelson Hi I haven't had a problem with rendering in HTML, can you share more details of what you are seeing and create a separate issue? @michaelquinn32