Move to Postgresql for channels, feeds and incoming (websub) data

[pstuifzand]

At the moment everything is inside the backend.json file or inside Redis. This structure has worked for a while, but now I think it is the time to move to an actual database to keep this information.

The code is written can be tested. It's available when you fetch the Go code with go get ....

I'm not sure how many people use Ekster on a daily basis and need it to be stable. So I would also like to make this the new version and then stabilize the releases.

If people have a problem with this, perhaps we can keep both "backends" and have a way to switch between them.

I like to hear your ideas.