Support to invite non-registered and registered users via email address. Contributions by ezra-g, lightsurge, and ymmatt. [#1097578]

This reverts commit 0cb27a28.

Missing patch hunks from http://ps.acquia.com/redmine/issues/1318 - og invite link user registration

Added admin-configurable email templates and og_notification integration for alerting admins of dispatched invitations.

Using theme('username') when showing names in messages, sending mails with user's preferred language, making the invitees field autocomplete, resolve a lot of coding standards issues with the coder module

Added additional validation of invitation acceptance. Prevented accepted invites from allowing a login for security purposes.