Improve download stats embed

[dlamkins]

It would look nicer if the redash embeds went all the way to the edge of the card and if we somehow used a dark mode. The hight is also kind of a random guess.

Perhaps Redash has an API that we can query this data from to give us better control in displaying it.

Example embed URL:
https://dashboards.blishhud.com/embed/query/21/visualization/32?api_key=WgbLIl20YAQQvaGy8khDWnCQSJ3dRt3loEJ1boip&p_$module_namespaces=${namespace}&p_RelativeDaysSince=15&hide_parameters=true&hide_header=true&hide_link=true

[dlamkins]

Additionally, since we don't scrape the prerelease repo, we don't dump download numbers into Redash for prereleases. This isn't normally all that noticeable, but for modules which have only ever had a prerelease, users will see a broken chart instead of what is actually expected: