Merge pull request #8066 from asutherland/email-land-imap-use-tcp-shim

Bug 814257 - [email] Move back-end into worker thread (speculative). groundwork, use node shims instead of mozTCPSocket. r=asuth, a=gal(cherry picked from commit 0f87a505a1b1972dff92de35a04ec618492f31c9)
Merge pull request #8070 from asutherland/email-explode-backend

Bug 814273 - [email] Replace concatenated gaia-email-opt.js with the files that make it up (as a vendor code drop). r=asuth(cherry picked from commit 02056c64bc15f879d5bdb1b4d02aa4b89bc4a5e7)