Change type of property to `vector<int>`

This allows readability of the property in graphml format. As vector
of integers is more specific than python object, I suspect this commit
also makes the code more efficient.

segments.py

@@ -35,7 +35,7 @@ t0 = t1
 
 # Processing:
 
-g.vp['inst_eddies'] = g.new_vp('object') # this object will be a list
+g.vp['inst_eddies'] = g.new_vp('vector<int>')
 print('Collapsing into segments...')
 g.set_fast_edge_removal()
 verts_to_del = []