Add generic converter plugin and python producer example for it

Implementation of a generic converter plugin that can be used by nonspecific DUT.
It is based on data conversion at producer and binary serialization using protocol buffers.
Added python example making use of it and fixes few issues related to python producer.

It is most likely not fastest but is suitable for small prototype devices. No need to touch any eudaq code to integrate (hopefully).

To enable need to install protocol buffers and add -DGEN_proto=ON to cmake command
This supports arbitrary size packages. Other way would need to add padding or use some other tricks. Would be easier if this would be done internally.

As far as I can see RawDataEvent uses vector<unsigned char> but I do not fully understand yet how this works.