webadmin: Rewrote Setup Networks operation logic

To extend the dragging capabilities in the Setup Networks dialog, the
following was done:

* Two new operations were introduced, JOIN_BONDS and
  EXTEND_BOND_WITH. Other null operations were added to better explain
  to the user what it is that went wrong.

* Completely rewrote the operationFor() method of
  NetworkOperationFactory. The main flow is now validation-oriented
  rather than operand-type-oriented, which enables to reuse the
  validation logic which is common to most operations (regardless of the
  operand type). Operand types are only checked secondarily, to know
  which specific operation to return once a network configuration is
  rendered valid/invalid.

* In order to better advise the user how to fix invalid network
  configurations when joining two NICs, the name of the network at fault
  is now saved in the NetworkInterfaceModel during the validity check,
  and later extracted using the getMessage() method of
  NetworkOperation. It's ugly but it works.

* Beautification: Standardized operation naming, error message naming,
  spacing in NetworkOperation enum.

* Changed some logic in HostSetupNetworksModel, specifically to enable
  reattaching all networks (of all NICs taking part in the bond
  operation) to a newly-created bond and to take special care of the new
  bond join operation.

* Changed some code in bond views to adjoin custom bond definition to
  the text in the list box, so that a user may differentiate between
  different custom bond options (if they exist).

Change-Id: Iea5793221d295fa0bd73fc1ed988c90df8fee7c8
Bug-Url: https://bugzilla.redhat.com/825801
Signed-off-by: Lior Vernia <lvernia@redhat.com>