Customize order of listing page entry pieces

[jmbuhr]

When I look at the narrow view of my and other distill websites I am having trouble discerning where each entry in the listing page starts and ends. I believe this is mainly because we are primed that headings and titles come first, followed by other content such as the preview image and tags. I am going to experiment with changing the order here:

https://github.com/rstudio/distill/blob/5beb7860d56530f7cbdda052c97c1357a94058a0/R/listing.R#L176-L189

Do you think this is something worth an additional parameter?