Allow severity levels of expert info items to be configured by the user.

UAT was the easiest way to do this and I like the "file format" of the data, but the presentation doesn't seem that great.

Bug:10180
Change-Id: I7e6bc9e148bc47585a0a7eb8f96900a5c374e673
Reviewed-on: https://code.wireshark.org/review/3082
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>