minor cleanup

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>
Add a wrapper between Seen_table and pymue.SeenTable

This is necessary because python-wrapped objects need a working copy
onstructor but mue::Seen_table is not copy-constructable. The wrapper
solves this problem by sharing one instance of the Table between all
Copies.

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>
Replace Seen_table with Seen_table_wrapper in the binding

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>