Futurize for python2/3

Context

This merge request brings compatibility for python 3 while ensuring backwards compatibility with python 2.

Details

The future package has been used to futurize the code. Waves can now depend on python3-xxx instead of python-xxx packages.

If python 2 is to be used instead of python 3, proceed with the usual build and add -DUSE_PY3=OFF to the cmake command line. Note that the additional python-futurize package is required.

Test

Passed on ubuntu18.04 (python 2.7.15 and 3.6.9), debian (gaston, python 2.7), msys2 (python 2.7.16 and 3.8.1)

mrstlnos/tests/beam.py

@@ -229,10 +229,11 @@ def main():
 
     slv.start()
 
-    from fwk.testing import *
-    tests = CTests()
-    tests.add(CTest('faked measure', 0, 0))
-    tests.run()
+    # [RB] this code is useless
+    #import fwk.testing as tst 
+    #tests = tst.CTests()
+    #tests.add(tst.CTest('faked measure', 0, 0))
+    #tests.run()
 
 if __name__ == "__main__":
     main()