Periodogram() should have power normalisation options

Problem description

I’ve received some feedback from Prof. Tim Bedding that units of Power Spectral Density are useful for solar-type oscillators, but not necessarily for other types. Power Spectral Density should be the default, but other types could be possible.

I’ll seek out some more community feedback before building a functional example.

Example

pg = lightcurve.to_periodogram(normalization="psd")

[barentsen]

I struggle to think of anything more exciting than @danielhey preparing a PR and @ojhall94 testing and reviewing it. ❤️

Note: over in #403 we just tinkered with the API to provide a generic Periodogram parent class and specific LombScarglePeriodogam and BoxLeastSquaresPeriodogram sub classes. The latter hold extra data and methods which are specific to those methods. I imagine psd normalization can go in the parent class (@christinahedges ?), but either way you will want to make sure to start a PR from the most recent version of the master branch because of these very recent changes! (They were made to add support for BLS to lightkurve.)

[ojhall94]

Hi Daniel,

If you wanted to do this one that would be great! You’ve got more experience on this topic so it would almost certainly turn out better than if I did it. Having it as a property is a neat idea, and a kwarg in from_lightcurve() was what I was thinking as well.

Cheers!