Implement rotated spectral PCA

[nicrie]

Is your feature request related to a problem? Please describe.
Missing spectral decomposition methods.

Describe the solution you'd like
Add the rotated spectral PCA method from this paper. They use the continuous analytic Morlet wavelet as a robust estimator of the cross-spectral matrices instead of relying on the Hilbert transformed data, which improves frequency separation.

Describe alternatives you've considered
None.

Additional context
None.