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>
DP-69 Add MessagingException base for all Cheddar messaging exceptions

Signed-off-by: Steffan Westcott <steffan.westcott@clicktravel.com>
Merge pull request #12 from clicktravel-steffan/master

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