Use SpinTaylorT4 by default for backwards spin evolution
The purpose of this MR is to use the SpinTaylorT4
approximant for the backwards spin evolution by default. This is because of a bug found by @nathan-johnson-mcdaniel in the SpinTaylorT5
approximant which is the default approximant used in the LALSimulation
function that pesummary
calls.
Edited by Charlie Hoy