Implement an internal Bookmarkmanager

[michael-simons]

The idea is to have an internal Bookmarkmanager similar to what SDN 6+ has: It shall do causal consistency by default and also can be disabled by a configurational flag in the URL, hence there should be a noop implementation and an implementation that actually does sent the bookmarks.

If the need arises that people want to access the last bookmark used on a connection, they can downcast Connection to Neo4jConnection and they shall find a corresponding method on that interface.