Draft: Implement CDTP in C++

The goal is to support two modes: either send a data frame directly, or create a message and attach as many data frames as you like, then send it.

For now, this MR does not implement this as a "hidden API", i.e. one needs to call the beginRun and endRun directly. However I have a plan to determine this at run time if the user inherits from DataSender.

TODO:

• Set filename on RawFileWriter
• Set (list of) subscriber(s) for DataReceiver
• Come up API for reaching SNDHWM
• Remove RCVHWM
• Check if we really need to close the socket on the receiver
• Add timeout if data senders are not found
• Add functionality to receive from multiple sources
• Add proper timer class (in utils?)
• Unit tests
• API for re-sending a message
• API docs