Add support for long running tasks

[Timmoth]

Each messages in a batch must finish processing before moving on to the next batch, in the case that a user has processes which take a considerable amount of time two problems occur:

• No more messages will be processed until the long running message is completed (for that specific processor instance)
• The transaction locking rows will remain open

To mitigate this issue we should add a flag on messages which allows users to specify if their consumers are are fast or slow, then handle each type of messages with a different processor, ensuring slow processes do not block fast processes.