alias raven_(animal) -> crow

BUR #7388 has been approved by @evazion.

create alias raven_(animal) -> crow

Before someone gets angry at me, I'm gonna quote wikipedia:

There is no consistent distinction between "crows" and "ravens", and these appellations have been assigned to different species chiefly on the basis of their size, crows generally being smaller than ravens

A raven is literally a large crow. We don't need two different tags for the same animal.

The bulk update request #7388 (forum #197547) has been approved by @evazion.

That's a rather bizarre line in the wikipedia article. The 'citation needed' after it is definitely justified. That said, for danbooru's purposes there's not really much of a difference so sure.