[MlMt] Mailbox Editor

[Randall Gellens]

I just updated to r6067 and the release notes contain:

> New: The mailbox editor supports opening a mailbox list making it 
> easier to review settings (sidebar icon to the left of the window 
> title).
> New: The mailbox editor has a filter button when the mailbox list is 
> open. This helps finding mailboxes with a specific type of settings, 
> in particular, rules.
> New: The mailbox editor has a unified title/toolbar. The type of 
> mailbox is now displayed below the name of the mailbox.

What is this mailbox editor and how is it different from double-clicking 
an individual mailbox? (If I select multiple mailboxes and edit them, 
there is a separate mailbox editor window for each).

--Randall