Support template replacements from data.

[almet]

  // Another example.
  {
    "kinto-emailer": {
      "sender": "Form Builder <noreply@kinto-storage.org>",
      "collection.created": {
        "template": "You've just created a new form. Here are the details: \n- {email.data.formURL}\n -{email.data.formAdminURL}"
        "recipients": ['{email.recipients}']
      },

      "record.created": {
        "template": ""
        "recipients": ['{email.recipients}']
      }
    }
  }

/buckets/{buck}/collections/{collection}/emails contains recipients, can be accessed only by people with the write permission on the collection.

[lavish205]

@almet need more information for working on this bug.

[Natim]

@lavish205 The problem we are trying to solve here, is a way to let people read the schema on the collection but without giving them the ability for reading the whole list of emails.

This is a bit related to #6