Create a NewsletterSubscription form object

* Add routes for newsletter subscription
* Update partial
Use partial in all the places
Add VCR and webmock
Merge with upstream changes
Add Newsletter Service
VCR the feature spec
Better newsletter params
Move list to env
Capture signup exceptions
Upgrade raven/sentry
Send exceptions to sentry
This didn’t work well. Reverting
Use fetch to get newletter params
Merge pull request #121 from gaslight/newsletter