Mean subtraction in FPCA

[igudav]

In FPCA the mean is subtracted twice: first explicitly by a _center_if_necessary function and then implicitly inside the sklearn PCA. The mean subtracted by the inner PCA is not a zero vector. Is it an intended behavior or the inner call should be to the TruncatedSVD method instead of the PCA?

[vnmabus]

@aleexarias As you are improving now the FPCA module, could you please take a look at this?