JNDI additions and ability to override the durable subscription prefix

I've re-forked and started again.  Changes are as follows:

Updated JNDI factory to allow specification of SNS and SQS endpoints, the SQSConnectorFactory class name, the max poll wait time and an override for the durable subscription prefix.

I've also updated the NevadoSession to use this prefix instead of the default if it is set.  Amazon seems to have an 80 character limit on the name of a subscriber and nevado_durable_topic took up a bit too much of that allocation for our needs.

I don't think I've changed anything that would require a unit test however, let me know and I'll try and create some.

Andy