Add integration tests for Send{Moderator,Subscriber}Email.cs

[dthaler]

AmazonSimpleEmailServiceClient will need to be mocked, to do so.

Rough sketch:

1. Create an Email Service Interface (IEmailService.cs)
2. Create an AwsEmailService.cs wrapper around AmazonSimpleEmailServiceClient that implements IEmailService.
3. Modify SendModeratorEmail.cs to use dependency injection.
4. Add SendModeratorEmailIntegrationTests.cs that mocks IEmailService.
5. Add SendSubscriberEmailIntegrationTests.cs that mocks IEmailService.