Bug 853757 - [Buri][Email/IMAP] Attachment names are not being MIME-word decoded. r=squib. a=blocking-b2g=tef+

land https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/174

does require copy-into-gaia.js fixup from:
https://github.com/mozilla-b2g/gaia-email-libs-and-more/pull/175