Add all shock response types as independent modes to `calc.shock.shock_spectrum`

Currently, `shock_spectrum` has a `mode` parameter that allows users to choose between calculating the SRS (`"srs"`) or the PVSS (`"pvss"`). With the addition of functions to `shock.py` for calculating the relative velocity, relative displacement, and relative displacement as static acceleration, modes for these additional spectra should also be added to `shock_spectrum`.