ATV.at: fix extractor using the new jwt JSON Web Token

[NeroBurner]

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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

Fix the ATV.at extractor as the site changed

Instead of using the external python module jwt from the python-jwt
package implement the web token creation is done following RFC7519.

The page uses a simmilar player as pro7 ans sat1, but different.

Fixes: #988

[NeroBurner]

How unique? For just the playlist currently downloaded, or for the whole site?

[pukkandan]

for the whole site. The download-archive works based on id.

Also, if a video can be downloaded through multiple URLs, all of them should give the same id

[NeroBurner]

I've got the following in the content variable

{
  "id":          "v-ce9cgn1e70n5",
  "tvShowId":    "745842",
  "tvShowTitle": "Bauer sucht Frau",
  "seasonId":    "s-cap22abg9hs9",
  "upc":         "v-ce9cgn1e70n5",
  "splitId":     "v-ce9cgn1e70n5-1"
}

I think the splitId field would be the best match. Would the other fields be useful for other extracted attributes?

[pukkandan]

only splitId and title seem usefull. But I believe u r already getting the title

PS: and id if you dnt already have a way of extracting the playlist's id

[NeroBurner]

rebased on current master and squashed commits