Fix a bug where some entries included the prompt

This sets the reply delimiter in Griddler, which tells it how to split
the user's response out from the original prompt.
Remove redundant tests

These cases are tested already in `spec/models/email_processor_spec.rb`.

The only thing we should really test in this file is Griddler behavior
before it hits the `EmailProcessor`.
Create an admin dashboard

Includes data on signups, entries, and trialing users' engagement.