Implement email sign-up

[jbuck]

After @adamlofting gets the sign-up list implemented in ET, I'll do the server-side implementation where we talk to ET.

[adamlofting]

Dev work can begin on this. The list is ready. The confirmation opt-in emails are not setup yet, but this doesn't block the dev.

Basket URL (connects to Exact Target Sandbox Account):

• Staging (connects to Exact Target Sandbox): https://basket.allizom.org/...
• Prod (connects to Exact Target Prod): https://basket.mozilla.org/...

Docs for subscriptions:

• http://basket.readthedocs.org/en/latest/newsletter_api.html#news-subscribe

Fields:

• newsletters: mozilla-foundation
• lang: de
• format: html
• optin: N
• source_url: {{URL_of_form}}
• trigger_welcome: N

No API key is needed as the list is double opt-in.

[jbuck]

Implementation in #38

[jbuck]

@adamlofting it looks like that newsletter hasn't been added to staging to production, but I tested with other newsletter codes and it worked fine.