Create subscriber API

[MarshallAsch]

Edit this may be changed to use a mailing list platform like mailjet or mailgun

This is to manage the people on the mailing list to be called from the admin page created in #31.

GET /api/v1/subscribers?offset=0&limit=20 to get the paged list of people on the mailing list
DELETE /api/v1/subscribers/:subscriberId to remove them from the list
POST /api/v1/subscribers to manually add someone to the list.

Note that when manually adding someone to the list it will override the email verification stage.
The post request will take a JSON object something like:

{
    "email": "email@example.com"
}