http2: Add additional header decoding information

This patch adds additional header decoding information, such as header
encoding representation, including header table size update (HPACK
draft-09, section 7).

Previously when user clicks the decoded header info, it highlights
wrong byte sequence in compressed pane.  This patch fixes this and now
clicking header will highlight the byte sequence it was decoded from.

Change-Id: I611a34edef31640c59a1f8bbc26db1c42eb16ce2
Reviewed-on: https://code.wireshark.org/review/3407
Petri-Dish: Evan Huus <eapache@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Evan Huus <eapache@gmail.com>