StatusView now allows the selecting of accounts through a MenuButton
with BitmapMenuItems― the button for selecting an account is nice and
discrete, just showing the bitmap of a protocol (in leiu of a label).
No functional changes, other than this menu.
I tried making all AccountsMenus use BitmapMenuItems, but that gets
unweildy pretty quickly― for now they remain in this menu. Maybe
optional ownership of bitmaps in BitmapMenuItems and caching of protocol
items would help.