Refactor modbus slave and Listeners. Handle each slave Type differently

[jmontanari]

• Refactor the ModbusSlave and Listeners. -- Abstract out the Unique attributes of each slave.
  -- Refactored the ModbusSlaveFactory to create and manage each slave type independently. -- Move the getProcessImage functions to each Listener. -- Use Type:IP:Port as unique Identification for slave mapping for TCP/UDP slaves and Type:SerialPortName as identification for Serial Slaves.

  • Remove the ThreadPool implementation and replace with an ExecutorService. The ThreadPool does not do anything special with threads. Ported from a fork of jamod i have.

[jmontanari]

This will break compatibility with previous releases for anyone who used the ModbusSlaveFactory.

[steveohara]

Because it breaks backwards compatibility, I need to combine this update with a retirement of the ModbusCoupler on a major release number change.

[steveohara]

This pull request has now been superseded by changes to the way in which process images are associated with slaves and the removal of ModbusCoupler If there are aspects of the pull request that are still relevant, please submit a new PR and I will take a look at it.