Raise better exception on InvalidParameterValue error

There are several reasons why we might get an `InvalidParameterValue`
from the SES API. One, as correctly identified before in
https://github.com/alphagov/notifications-api/pull/713/files
is if we allow an email address on our side that SES rejects.

However, there are other types of errors that could cause an
`InvalidParameterValue`. One example is a `Header too long: 'Subject'`
error that we have seen happen in production. This shouldn't raise an
`InvalidEmailError` as that is not appropriate.

Therefore, we introduce a new exception
`EmailClientNonRetryableException`, that represents any exception back
from an email client that we can use whenever we get a
`InvalidParameterValue` error.

Note, I chose `EmailClientNonRetryableException` rather than
`SESClientNonRetryableException` as our code needs to catch this
exception and it shouldn't be aware of what email client is being used,
it just needs to know that it came from one of the email clients (if in
time we have more than one).

In time, we may wish to extend the approach of having generic
`EmailClient` exceptions and `SMSClient` exceptions as this should be
the most extendable pattern and a good abstraction.

app/clients/email/aws_ses.py

@@ -5,7 +5,7 @@ from time import monotonic
 from notifications_utils.recipients import InvalidEmailError
 
 from app.clients import STATISTICS_DELIVERED, STATISTICS_FAILURE
-from app.clients.email import (EmailClientException, EmailClient)
+from app.clients.email import EmailClient, EmailClientException, EmailClientNonRetryableException
 
 ses_response_map = {
     'Permanent': {
@@ -122,7 +122,7 @@ class AwsSesClient(EmailClient):
 
             # http://docs.aws.amazon.com/ses/latest/DeveloperGuide/api-error-codes.html
             if e.response['Error']['Code'] == 'InvalidParameterValue':
-                raise InvalidEmailError(str(e))
+                raise EmailClientNonRetryableException(str(e))
             elif (
                 e.response['Error']['Code'] == 'Throttling'
                 and e.response['Error']['Message'] == 'Maximum sending rate exceeded.'