Bug 869817 - [Email] "Last Sync:" value at folder screen is not displayed properly with IMAP accounts. r=asuth

Land:
https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/203

This includes a required review fix of changing erroneous use of 'this' in a
forEach in FolderPickerCard.onFoldersSplice to 'self'.  This corrects the
problem where the value is not displayed at startup.