Distinguish between SendGrid API credentials and event handler
credentials

The SendGrid event handler was reusing the SendGrid API credentials. I
decided this was a bad idea and it should have its own credentials, as
they will probably be less secure.
Merge branch 'feature/sendgrid_events' into develop-fftf
Render SendGrid email stats alongside Platform stats
Fix typo
Clean up template
Grabbing email_id from Sendgrid