Add thumbnail independent hidden badge

[mxmeinhold]

Currently, in the directory view, the only indicator that an image is hidden is a slight greying, which is a poor indicator on images that are primarily grey.

This adds a badge to make it obvious.

TODO

• Test on dev
• Upload screenshots

Resolves #54

[adamhb123]

Evaluated to be functional in a local dev environment.

Badge shows properly, though it increases the height of the image container
Screenshot (blur added in post):

The only way to fix this is either change the way the images are structured so as to allow space for badges, or position the badge absolutely.

I think it would be better both stylistically and pragmatically to do something like the following (quick drafts, with blur added in post):

This method indicates the fact that the image is hidden in the filename section, as well as having obvious, simple styling indicating that the image is unique.

Coloring could be adjusted to be more appealing, obviously (the contrast in the left image is egregious to say the least).