Impement a waveform-less read-in

[fschlueter]

Reading in runs without the waveform would allow fast calculation of, for example, trigger type depending trigger rates. This could be useful for monitoring. Other properties of the daq included. @cozzyd what do you think?

[sjoerd-bouma]

As mentioned in #64, I think the way forward would be to have skip_incomplete=False

• [ ] 1. be able to read in all header info if only some of the waveforms are present - this used to work but broke in #54
• [ ] 2. read in header info if no waveforms are present - this never worked, but seems like a reasonable extension of 1. and would be useful to have.

I think that should do what you want it to do here - I certainly already used 1. for the RNO-G data monitor until it broke.

(This is just me supporting your feature request, not demanding you implement it or - unfortunately - offering to implement it ;)