Make fetchers web-based

[koppor]

We have fetchers with API key and screen scraping. For the screen scapers, they mostly don't work. We should switch to a browser-based screen-scraping. Mostly because of CloudFlare.

Maybe the Java Chromium Embedded Framework (JCEF) helps. The test class https://github.com/chromiumembedded/java-cef/blob/master/java/tests/detailed/handler/RequestHandler.java seems to guide one to the usage.

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The PR JabRef#7075 attempted to display the Google Scholar captchas in JabRef. The PR was not completed. -- This issue says: Rewrite the fetchers not to use URLDownload, but JCEF.

Note that this is different from JabRef#11093. There, a new UI is demanded.

Here, the it should be allowed that the fetchers run stand-alone without user interaction.

[koppor]

Duplicate of JabRef#11093