Cache images and serve thumbnails

[HeroicEric]

The idea is to fetch and store the images associated with each podcast and episode in order to serve different versions of the artwork.

Maybe use https://github.com/stavro/arc?

• [ ] Fetch and store images
• [ ] Provide a placeholder when images are not present
• [ ] Generate thumbnails
• [ ] Configure storage to work with Amazon S3
  • [ ] Configure Access Control Permissions
• [ ] Limit file sizes
• [ ] File Validation
• [ ] Configure file naming scheme https://github.com/stavro/arc#file-names

[HeroicEric]

https://github.com/stavro/arc/issues/1#issuecomment-229767814