add w2lists_def readout

Add function to automatically read out w2list_XXX_idx from definitions for an offline file

src/km3io/tools.py

@@ -539,7 +539,7 @@ def is_3dmuon(trigger_mask):
     return is_bit_set(trigger_mask, ktrg.JTRIGGER3DMUON)
 
 
-def get_w2defs_idx(f):
+def get_w2list_idx(f):
     """
     Get the correct w2list_idx for the given file, or None if there is none.