Add support for 'subplots' from plot_ly and ggplotly in DashR

[rpkyle]

As pointed out by @sacul-git in #83, DashR would fail to properly mutate plot_ly and ggplotly objects constructed using the subplots function from the plotly R package.

The changes proposed in this PR change the logic for mutating the layout in encode_plotly; now, the function will

• introspect the object to check to see if it is a list; if it is, then
• check to see if the object class attributes include plotly; if they do, then
• check to see if the list contains a named element x; if it does, then
• check to see if any names within x match visdat or data; if they do, mutate

dashR/R/utils.R

Lines 579 to 582 in 5264c7c

	if (is.list(layout_objs)) {
	if ("plotly" %in% class(layout_objs) &&
	"x" %in% names(layout_objs) &&
	any(c("visdat", "data") %in% names(layout_objs$x))) {

[alexcjohnson]

Beautiful 💃