Improve Pleroma support

[austinhuang0131]

• Interacting with status (using the favourite/announce buttons). Note that the Testing guide in the wiki needs to be updated too.
• Username detection using request body.

Feel free to only merge one commit. I'll add contributor credit after your approval.

^{Yes, I'm aware that I'm PR'ing from the master branch, but GitHub has a "fetch origin" button online now, so it's all good}

[rugk]

Hi @austinhuang0131,
first of all, thanks for your first contribution to this project! 🎉 👍 🏅
I hope you'll like this project and enjoy hacking on it… 😃

So yeah, this looks like a good improvement (though I have not tested it in practice.)

About the master branch: Yeah, sure feel free to do what you want. The only reason I always suggest a separate branch is so that you can have separate PRs. If you now e.g. would want to create a separate PR or this one would not be accepted/you'd close this, you would have all these commits in the main branch of your fork, which is unfortunate, as you would have to rewrite the history in a quite cumbersome way to get it right and start with a "fresh" branch from upstream. I know, yeah, there are other solutions, but for beginners I always suggest this to keep it clean and in shape.

[rugk]

Just some minor thing.