Contacts dealing in roster

Here is an UML diagram about how we deal with deal with contacts in roster_window.py

Note that there are not any classes in the diagram. It's is only to understand how roster make differences about rows in the code, for MetaContacts handling. meta contact is a logical entity, it doesn't exist in the code but everything done about contacts that are part of it should take care about it. Pay special attention to cardinalities.

Comments and corrections welcome.