Feed duplication

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The implementation was done in a more of personal look, so I did not think about this while development.

At the moment, we are checking if the feed already exists for current channel, this is fine, but we would need to extend this logic.
One can add the same feed url many times, this would mean the app would load the same feed n times over and over, although on a different channel. This is obviously a waste of resources.

We need a way, to determine if the feed already exists (it does not matter if on a different channel) and just reuse that, instead of loading the same feed many times, we would do this once only and improve the process.