DP-69 Continue SQS message processing loop if malformed message received

Fix a bug where receiving an SQS message that cannot be parsed as a Cheddar SimpleMessage would terminate the SQS message processing loop.

Signed-off-by: Steffan Westcott <steffan.westcott@clicktravel.com>
As its internal to SqsMessageProcessor, its unnecessary to add MessageParsingException. The idea to add abstract base class MessagingException is good, so I've implemented that.