Add cover images to all snippets

[Angelos Chalaris]

For SEO and overall aesthetic purposes, we could expand the cover image mechanism to all snippets. This will require roughly the following:

• Move all assets to their own repository where we can reuse them easily and get their metadata as necessary.
• Replace existing assets with lower quality ones (not the actual output images).
• Create a proper mechanism for image credits that will inject the data into the snippet.
• Update blogs to use the new mechanisms.
• Update designs with the new covers.
• Update all snippets to use covers.

[Angelos Chalaris]

After further investigation, this project is going to be scrapped. Any mocks we've tried with images, patterns, colors etc. result in distractions for the users and less accessible content. We'll keep using images in blog content only for the time being.