Computes the Lomb Scargle Periodogram and returns the information needed for computing the DFC and HP. A plot visualizing the Harmonic Frequencies presence in the spectrum is possible. The function is inspired from the Lomb library in a great part, with modifications to fit the requirements of harmonic powers and computation of the DFC. This function is inspired by the lsp function from the lomb package and adapted to add different colors for harmonic and non harmonic frequencies in the signal. For more information about lomb::lsp, please refer to: https://cran.r-project.org/web/packages/lomb/