webadmin, userportal: logical network editor

Added a possibility to assign logical network to nic
in new/edit VM popup.

The specific behavior:
- it is present only in new/edit VM (not in pool/template)
- on new VM, if there is no NIC on the template the VM is based
  on (such as Blank) than create one new nic.
- if there is some, use the ones from the template letting the
  user to assign the logical network
- there is a possibility to not assign a network to a nic (if the
  cluster supports it). It is visualized as empty line in the combo
- there is no way to create a new VM without at least one
  network interface - even there is still a possibility to delete
  the created one

The common code from the new/edit network interface dialogs has
been extracted to behavior classes.
The common code between VmListModel and UserPortalListModel has
been implemented in VmNetworkCreatingManager.

Change-Id: I8a5b488236ba5a08fc9050ed13a6ed49802769da
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>