webadmin: Setup Host Networks Feature

This feature allows the editing of a Host Network Topology.
All topology changes are done on the dialog, and sent in one request to the backend.

The implementation uses Models and Views to manipulate the Following Networking Items:

* Network Interface Card (physical nic on the Host)
* Channel Bond (defined on the Host)
* Logical Network (network defined on the cluster level)

Models:

NetworkItemModel
 |
 +--LogicalNetworkModel
 |
 +--NetworkInterfaceModel
     |
     +--BondNetworkInterfaceModel

Views:

NetworkItemPanel
 |
 +--NetworkPanel
 |
 +--NicPanel
     |
     +--BondPanel

* Interactions between the Models are done using Network Operations.
* The Operations are defined as static enums, and operate on two operands.
* When the Operation is Unary, the second operand is null;

Following is a list of Operations, with the expected Operand Types:

+------------------+---------------------------+---------------------------+
| Operation        | Operand 1                 |  Operand 2                |
+------------------+---------------------------+---------------------------+
| BREAK_BOND       | BondNetworkInterfaceModel | null                      |
| DETACH_NETWORK   | LogicalNetworkModel       | null                      |
| ATTACH_NETWORK   | LogicalNetworkModel       | NetworkInterfaceModel     |
| BOND_WITH        | NetworkInterfaceModel     | NetworkInterfaceModel     |
| ADD_TO_BOND      | NetworkInterfaceModel     | BondNetworkInterfaceModel |
| REMOVE_FROM_BOND | NetworkInterfaceModel     | null                      |
| NULL_OPERATION   | null                      | null                      |
+------------------+---------------------------+---------------------------+

* The Operations can be activated through Drag & Drop, or through a context menu.
* An Operation Factory is responsible for resolving a valid Operation for any two given Operands.
* Result might be the NULL_OPERATION.
* The same is also responsible for calculating a Matrix of possible Operations for a given Network topology
  (to be used in context menus).

====================================================
Additional Changes (required by the implementation):

* UICommand: Add Executing with parameters.
* UICommand: Add IsVisible property.
* TabModelProvider: allow resolving the View according to a Model, in addition to the last executed command.
* Fix a bug in the UiCommonEditorVisitor when there is already a Selected Item.
* Add a Status Widget tot the Popup View
* Mkae sure Popup contents are scrolled in case of overflow

Drag & Drop support:
====================================================
Using HTML5 DnD specification:
http://www.w3.org/TR/html5/dnd.html

HTML5 DnD is supported by standard complaint browsers (Chrome and Firefox, and IE9).
IE8 does not support it (has it's own DnD mechanism) - IE8 users will have to use the context menu.

Since this was implemented only in GWT 2.4, I copied the Event classes, and did the event sinking in the DnDPanel.

IMPORTANT: when upgrading to 2.4, remove the classes in the "com.google.gwt.event.dom.client" and "com.google.gwt.dom.client" packages,
           as well as the DnDPanel.

Change-Id: I2b79c1e02f38c2e2078a5ad19dcc7a4d7f2232ea