Change reference distance and interpolant behavior

When setting the minimum of the distance prior to extremely small values (like 1 Mpc to match the LALInference behavior) this leads to huge values of the reference SNRs stored in the lookup table for distance marginalization. The interpolation of the lookup table was also not verifying that the interpolated values are inside the bounds for which it was initialized, leading again to huge values of the SNRs and likelihood. This MR changes the reference distance to be the median of the prior instead of the minimum, and throws an error when the interpolation tries to exceed the bounds.