GTK: Unlimited, dynamically allocated IO Graph

Bug: 8460
Change-Id: Id9aad3f5f69bee9e5a62601ecac28a6a7019e623
Reviewed-on: https://code.wireshark.org/review/2672
Reviewed-by: Evan Huus <eapache@gmail.com>
Reviewed-by: Graham Bloice <graham.bloice@trihedral.com>
Reviewed-by: Balint Reczey <balint@balintreczey.hu>