Refactor DCE/RPC dissection to include a real dissector table.

Refactor DCE/RPC dissection to include a real dissector table.

This is hopefully just the first step in getting DCE/RPC dissection to use "standard" APIs instead of homegrown ones.
For starters, it allows Decode As functionality to be less hacky (although incomplete in Qt)

Change-Id: Ia0923a3d8d514ab7acce32e26ee7e08f6e24feca
Reviewed-on: https://code.wireshark.org/review/11468
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>