Add option to save copy of reply in same mailbox as original message

[ianeiloart]

Mulberry offers various options for saving sent messages:

Copy to: (a preselected mailbox)
No copy
Choose copy to

It would be nice to add:

When replying, save with original message
Save to selected mailbox

In this way, entire conversations are saved in the same mailbox - think Gmail!

Currently, this is only doable with complex association of identities with individual mailboxes, and there's no way to achieve it if an identity is associated with multiple mailboxes - except by duplicating identities.