Handle webcal prefix in remote calendar

[Thomas55555]

Breaking change

Proposed change

There was a response from a user, which tried to add a webcal URL in the beta to the calendar.
The prefix webcal:// just tells the browser to download a the file. The actual destination is normally just an http server.
So we assume that the proper prefix must be https://
As an alternative we could also just display an error message, for the user which tells him to find a proper url?

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• Dependency upgrade
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• This PR fixes or closes issue: fixes #
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[frenck]

Thanks, @Thomas55555 👍

../Frenck