Consider allow .castor directory as alternative to castor

[ruudk]

For example, GitHub follows this with .github folder.

Makes it clear it's not related to the project.

[lyrixx]

We changed to castor at the very beginning. I was not really convinced...

I prefer .castor too!

I'll see what I can do if the core team is okay with this move

[pyrech]

Both have pros and cons.

But as we will soon have a .castor directory when using remote import, I think it's fair to look natively for tasks in the .castor directory too 👍. I think we can support both naming out of the box.