Bug 709561 - Pick up Windows Live mail from GOA

This adds an "outlook-backend" module, similar to the "google-backend"
and "yahoo-backend" modules.

Outlook.com recently added IMAP support, and GNOME Online Accounts now
exports a "Mail" interface on its "Windows Live" accounts.  This module
configures an E-D-S IMAP/SMTP account bound to the GOA account.