Add CI with python 3 including trilinos

This Merge request adds a python3 build with the corresponding tests to the current CI pipeline.

A docker image including Trilinos has been created for this purpose.

Some remaining minor compatibility issues with python 3 have been fixed.

tbox/utils.py

@@ -80,10 +80,11 @@ def read(filename):
     """Read from file and store in data array
     Adrien Croavto
     """
+    import io
     import numpy as np
     # read file
-    fl = file(filename)
-    label = fl.next().split(',')
+    fl = io.open(filename, 'r')
+    label = fl.readline().split(',')
     fl.close()
     data = np.loadtxt(filename, delimiter=',', skiprows=1)
     return data