Select blank card thumbnails from random pool of thumbnails

[JHay0112]

Problem:
Articles that have no thumbnail look boring and could be confused for a broken image.

Proposed Resolution:
It would be better to have a thumbnail that is generic but more visually interesting than the grey box that is currently used.

Requirements:

1. Articles without a thumbnail shall be randomly assigned a thumbnail from a set of predefined images.
2. Random thumbnails shall be more visually creative than a blank grey box whilst remaining minimally distracting from the content.
3. Random thumbnails shall be generic enough to be used with most potential topics.
4. Articles shall have the same random thumbnail for their lifetime.
5. Articles may share the same random thumbnail, provided not all articles use the same thumbnail.

[JHay0112]

No longer relevant, replaced cards with "books"