The energy_loss and power_loss_spectrum methods for ImpedanceModel can now take any bunch spectrum in optional agrument.
Add bunch_spectrum and plot_bunch_spectrum to BeamLoadingEquilibrium.
Apply formatters and update notebook

Update CavityResonator and collective effects notebooks.

Add a new example notebook on RF cavities and longitudinal beam dynamics which explain the RFCavity, CavityResonator and BeamLoadingEquilibrium classes.