webadmin: Add QoS button in Add/Edit Network dialog

Added the ability to add a new QoS entity through the Add/Edit Network
dialog, in case no fitting QoS entity exists.

Change-Id: Ia62cb0da531a06c782d9d753f46bb9f7c48a5b9a
Signed-off-by: Lior Vernia <lvernia@redhat.com>