Consider adding thumbnail images for news items

[krivard]

A blog file specifies a hero image in its header:

www-main/content/blog/2015-07-23-template-post.Rmd

Line 14 in 1287604

heroImageThumb: blog-thumb.jpg # size: 300x300 jpg format

A news file does not:

www-main/content/about/news/headless/2016_12.md

Lines 2 to 4 in 1287604

	date: 2016-12-01
	title: Delphi Wins 2015-2016 Forecasting Challenge
	category: accomplishment

This means that when the landing page formulates its "latest news" section, it can grab a unique thumbnail image for each recent blog post, but is stuck with the placeholder-thumb "D" logo for each recent news item:

via

www-main/themes/delphi/layouts/partials/landing/latest-news.html

Lines 4 to 12 in 1287604

	{{ define "partials/latest-blog" }}
	{{ return (dict "source" "blog" "img" (($.GetPage "/blog/images").Resources.GetMatch .Params.heroImageThumb) "title" .Title "link" .RelPermalink "date" .PublishDate "summary" "" ) }}
	{{ end }}
	{{ $items := apply (.Site.GetPage "/blog").Pages "partial" "latest-blog" "." }}
	{{ define "partials/latest-news-item" }}
	{{ return (dict "source" "news" "img" (resources.Get "/images/placeholder-thumb.jpg") "title" .Title "date" .PublishDate "link" (.Site.GetPage "/about/news").RelPermalink "summary" (.Summary | safeHTML | truncate 100) ) }}
	{{ end }}
	{{ $newsItems := apply ((.Site.GetPage "/about/news/headless").Resources.ByType "page") "partial" "latest-news-item" "." }}

To make it so that the "latest news" section on the landing page can display a more useful thumbnail for news items, we need to:

1. Pick a new parameter name for news item thumbnail images
2. Add this parameter to all existing news item pages (possibly just pointing to the placeholder-thumb)
3. Upload thumbnails for all existing news items not specifying the placeholder-thumb
4. Update the latest-news template with something like ($.GetPage "/blog/images").Resources.GetMatch .Params.heroImageThumb instead of resources.Get "/images/placeholder-thumb.jpg"
5. See if it works & fix it until it does

If we additionally want to display the thumbnail on the news listing page (https://delphi.cmu.edu/about/news/), we'd need to update the news item template, possibly based on the blog card template. This would however be more complicated and we might need to pull in sam.