Experimental filters

Feature creep never ends. Added a very limited filter function, which can rewrite or edit posts. There's a couple ad hoc filters already, but this should converge over time.

There was already a tiny link normalizer, which only worked for youtube, which I find helpful to keep consistent URLs. And then it also rewrites lemmy links to self hosted images, which shouldn't (imo) appear as links.

The next problem I had is sometimes people post links, but put the link in the body, not in the link section where it belongs. This annoys me. I can't immediately see what site the link is for. It looks like a self post, then I open it, and then I have to open another link. That's two clicks! We can find a link in the body and make it the post link pretty easily.

But not all the time. I think that would result in too many false positives. So I started work on a little filter engine, that matches and alters posts. It's very limited at the moment, to only this use case, but the parts are now there for more extension.