Bug 824930 - Enable newsletter even without connection (r=etienne)

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- Delete the specific newsletter button, and use navigation Next for it
- Error if email not valid
- Send if connection available
- Store locally if no connection
- Try to send it again when Dialer is idle for 5s
Merge pull request #8622 from fcampo/emailConnection

Bug 824930 - Enable newsletter even without connection (r=etienne)