plot_pt_bounds: Add point estimate bounds to a plot list
In sakrejda/pager: Spread ggplots over multiple pages

For each plot in .pl, add a plot IFF the grouping factor in 'data' has a matching level (when used with 'as.character').

1	plot_pt_bounds(.pl, data, time, lb, ub, group, ...)

`.pl`	plot list, generate with 'plot_list' and pipe in.
`data`	data for time-series plots
`time`	bare name of the time-axis column
`lb`	bare name of the lower bound column.
`ub`	bare name of the upper bound column.
`group`	bare name of the variable to use to split plots on.