I have been thinking about the run number we currently have defined as the payload for the `start` transition, and I have two related questions: * [ ] Wouldn't it be nicer to be more flexible in providing a run identifier than an unsigned integer? I could very well imagine some people wanting to use ISO dates followed by a sequence number, or name them according to the measurement they are doing. Hence a string might be more flexible? * [ ] We currently do not have a way of retrieving the current run number / identifier while in the `RUN` state. We should add this because otherwise a newly joined controller does not have any way of obtaining the current run number.