WEBSITE-266 update email subject line to include [grails.org]

also changed "tab" to "section" in subject.

test email using greenmail:

![screenshot](https://www.evernote.com/shard/s3/sh/122acb4e-19de-4a7c-8c5e-2968f56cc6c8/b92f82743d70a7c9f3a85ff0f8712d24/deep/0/Screenshot%208/17/13%2011:27%20PM.jpg)