`kafka_dae_diagnostics`: handle frame headers & periods

[Tom-Willemsen]

To allow publishing statistics like:

• Frame counters
• PPP
• Integrated beam current
• Per-period versions of many existing/above statistics
• Per-period spectra

We need to handle frame headers and assign each ev44 to it's corresponding frame header. At the time of writing, the frame headers are not being streamed and the format has not been finalised.

[Tom-Willemsen]

Don't pick up until #37 is done, then review how much of this is still necessary.