Clean up wallpaper providers

Kat Pavlurequested to merge
katp/kdeplasma-addons:fix-wallpaper-providers into master

BUG: 505425 BUG: 505430

  • Remove NOAA Picture of the Day provider
    • The NOAA blog recently changed the type of content they post on their daily blog. Abot 50% of the posts now include a video instead of an image. Nate Graham recommended the plugin be removed in the linked issue.
  • Fix the EPOD provider (there was a regexp issue)
  • update documentation

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