Add option to turn off "Share the list by email" to anonymous users

Rather than hiding the sharing functionality from anonymous users, we should give the option for how to handle this.

Anonymous sharing of a list should be possible. You should be able to share a direct link to a Wishlist and have an email sent off that contains the link.

Anonymous sharing should be able to be disabled. i.e. admin should be able to turn off anonymous sharing and require that someone be logged in in order to share via email

Additional functionality added to create a configurable option to allow anonymous Wishlists when shared by email, to be duplicated and Wishlist items added to the new Wishlist. The duplicated Wishlist is the one that is emailed to the recipient.

I've tested the fix from the MR. It works.

Automatically closed - issue fixed for 2 weeks with no activity.