GiBUU weight in W2List

In order to provide more information from the actual GiBUU run used for writing the KM3NeT file, I suggest to write the GiBUU event weight also to the KM3NeT file. The definition of the w2list was applied from gSeaGen and the additional field will be added, which will conserve the full compatibility of the files.

km3buu/tests/test_output.py

@@ -130,3 +130,5 @@ class TestAANET(unittest.TestCase):
         np.testing.assert_equal(evt.w2list[9], 34)
         # CC/NC
         np.testing.assert_equal(evt.w2list[10], 2)
+        # GiBUU weight
+        np.testing.assert_almost_equal(evt.w2list[19], 0.8167222969153614)