trust: Refactor to include concept of the index

trust: Refactor to include concept of the index

 * The index holds PKCS#11 objects whether for the token or for the session.
 * The index provides hook for a builder to expand or validate objects
   being added to the index.
 * In addition theres a change hook so that a builder can maintain state
   between objects, such as the compat NSS trust objects.

https://bugs.freedesktop.org/show_bug.cgi?id=62329