Logging / Tracing / Debugging facilities

[C0nsultant]

In order to better understand the internal flow when debugging or developing, it would be very helpful to have run-time switchable logging, including debugging and tracing levels.

For a simple and fast solution, https://github.com/gabime/spdlog could be a good option.
More ready-made C++ logging facilities are available.

[ax3l]

From #460 (comment):

We abstracted [...] quite far so that many IOTasks can not be identified with simple names anymore. What I found helpful is to add debug info to the task switch boards in AbstractIOHandlerImpl and potentially their equivalents in ADIOS1IOHandler/HDF5IOHandler/JSONIOHandler.