Merge "fin" and "fins"

fin is implied by dorsal fin and has been tagged almost exclusively by a BP over the course of the last year
fins is implied by tail fin and fin wings, and has been used by other people (as well as a lot by that BP who seems to have a targeted interest in underwater creatures)

So, it would probably be right to alias fin -> fins and then update dorsal fin to imply fins instead of fin

Typically plural tags alias into singular form, tho I’m not sure which is better here.

@LightningBolt
I thought it was the other way around, eg. wings has wing aliased to it.

@Background Pony #0D6D
Well, wings do come in sets typically…