Rename our concept of "flair" in the code

[Sjmarf]

In the code, we use the term "flair" to refer to these things next to the username:

Both Lemmy and PieFed now have their own features called "flairs". We should rename ours internally to avoid the naming conflict. Maybe "badge" is a good alternative?

We also use the term "tag" when referring to the icons in post titles. We could rename those to "badges" too.

[sunshinehot]

Yes, badge is good!