This commit uses the low-pass filtering introduced in the latest PR to SQuIDS. This low-pass filtering can be applied while integrating the interaction picture states over time by calling
`Set_EvolLowPassCutoff` to choose a cut-off frequency of the filter. The frequency has units 1/length. This filter can speed up calculation of interaction picture states significantly in the presence of
eV-scale sterile neutrinos.

There are a few more additions to the Python interface of `nuSQUIDSLayers` that allow the filter to be applied also when projecting out probabilities from interpolated states.

… mode

Pybindings are greatly improved with overloads instead of differently named
functions, with doc-strings for the most important methods.

Preparations have been made to enable `both` mode to propagate neutrinos
and antineutrinos in the future. Work to enable it properly are still
ongoing.

The single-energy mode of nuSQuIDS is now initialized in the same way
as for the multiple-energy mode. This enables propagation of neutrinos
and antineutrinos at the same time.

Pybindings for nusquids layers have been improved further to allow
passing of different averaging ranges for every event.