Wrap notmuch_thread_get_oldest_date() and notmuch_thread_get_newest_date()
Wrap basic thread messages retrieval and traversal functionality

Namely:

    -   notmuch_thread_get_messages()
    -   notmuch_messages_valid()
    -   notmuch_messages_get()
    -   notmuch_messages_move_to_next()
    -   notmuch_messages_destroy()
Clean up tests
Wrap notmuch_query_search_messages()
Wrap notmuch_thread_get_toplevel_messages()