Removed the unused icon field.
Revert "Removed the unused icon field."

This reverts commit d89a2cc5ab39b702ee4c4bf2258df7217c6a9e6b.
New fix for the 'field never assigned to' problem.
Merge branch 'xwt_upgrade'

Conflicts:
	Xwt/Xwt/WindowFrame.cs
Automatic scrolling to selected element in ListView implemented.
Insensitive buttons with Image made grayed out.
Hack that makes multiselect and right-click on ListView working.
Icons centered in ListView cells.
Glitches when right-clicking on multiselected ListView resolved.
DialogButton made inheritable.
Escaping undescore in notebook tab label.
Add support for rendering images into a native surface object
Add some Menu docs
Add support for multi-size icons

And added support for that in the GTK backend.
[GTK] Properly scale stock icons
[GTK] Added support for creating an image from a stockId
Add Width and Height properties to Image
[GTK] Fix stock icon rendering issues
Fix for bug #220. Xwt.Gtk editable checkbox cell views did not work properly.
Merge https://github.com/mono/xwt into HEAD