Part of Bug 443351 Move all of Thunderbird's unofficial/nightly branding items into mail/branding/nightly - more moves and fix official branding bustage. r=mkmelin
--HG--
rename : mail/app/icons/gtk/messengerWindow.xpm => mail/branding/nightly/gtk/messengerWindow.xpm
rename : mail/app/icons/gtk/messengerWindow16.xpm => mail/branding/nightly/gtk/messengerWindow16.xpm
rename : mail/app/icons/os2/messengerWindow.ico => mail/branding/nightly/os2/messengerWindow.ico
rename : mail/app/icons/windows/messengerWindow.ico => mail/branding/nightly/windows/messengerWindow.ico