webadmin: Add HostNetworkQos widget

Added model and view for a reusable host network QoS widget, to be
used when overriding QoS configuration on a specific host interface
and in a dialog of its own (same as other QoS entities).

Change-Id: I6a97c260ba18d21d911a0338149fefc2c6222c52
Signed-off-by: Lior Vernia <lvernia@redhat.com>