Refactor "common" hostlist/endpoint table functionality.

This is very similar in architecture to the changes made to the Conversation table functionality.  Since all conversations have endpoints/hostlists, the "registered" list is shared for both.

Change-Id: Ie8c6910a68a1b3f27c5b18c4494f49b9404a7b31
Reviewed-on: https://code.wireshark.org/review/3214
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>