PLC4J SPI Rewrite

In contrast to PLC4C, PLC4Go nad PLC4Py, PLC4J relies highly on third party frameworks for providing the ReadBuffers and the internal workings of the Drivers. Here most of all Netty has been causing a lot of problems recently. 

We want to rewrite our Read- and WriteBuffers to work without external dependencies and we want to crearte a new driver core, that works without Netty and allows features we have been struggling to support. Features such as:
- Multiple low-level connections for one PlcConnection
- Allowing sharing of resources, such as Serial ports and listening UDP ports to allow addressing multiple Modbus RTU devices that are attached to one RS485 port or communicating with multiple BacNetIP devices simultaneously

The reduction of external dependencies, especially ones as complex as Netty, will become a requirement in upcoming times, where CRA and PLD dictate us to be a lot more explicit about security. Only reducing external dependencies to the absolute minimum will prepare us for what's to come.