Port to python3 and new lalsuite

Hi Greg, I've recently been playing around with pyFstat, and wanted to update/modernize various aspects a bit.

If you're happy to integrate such changes into your upstream repo, I'll send you a few merge-requests, otherwise I'm also ok to keep this stuff on my fork.

pyfstat/grid_based_searches.py

@@ -12,7 +12,7 @@ import socket
 import numpy as np
 import matplotlib
 import matplotlib.pyplot as plt
-from scipy.misc import logsumexp
+from scipy.special import logsumexp
 
 import pyfstat.helper_functions as helper_functions
 from pyfstat.core import (BaseSearchClass, ComputeFstat,