Support "Export data" from R visuals

Here's an example of when this would be useful: I can quickly create a number of boxplots using R. But once something interesting is found in the data, users will want the output from boxplot.stats -- the statistics from the boxplots. There's no easy way to get those boxplot.stats except through a huge kludge. This was a great help: R graphs and tables in Power BI Desktop, https://tomaztsql.wordpress.com/2016/12/18/r-graphs-and-tables-in-power-bi-desktop/ A second R visual can repeat all the boxplot computations with plot=FALSE specified, and then the stats can be captured and plotted as text in a graphic. The data table as a graphic prevents copying and pasting the data, which is a huge kludge but that makes the data visible. Even better, let us use R to create new Power Bi datasets that can be used in Power BI visuals -- or even other R visuals.