Included image cards no longer obey CSS rules+discussion

More information to help locate the cause:

- The most recent Internet Archive snapshot of the Image card on wagn.org is 2017-09-19. Unfortunately, the page didn't say which version of wagn the site was running.

- As for wagn running on my site, I didn't keep a record of when I upgraded the wagn gem, only that I upgraded it at least once between 2016-10-26 and 2017-02-22 based on the Internet Archive's snapshots, and I went more than a year before noticing that the problem was present and unreported.