Bug 176882 [DataBinding] Create SWTObservables.observeEditable(...)
We need to provide an observable for the editable property of Text.
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/databinding/swt/SWTObservables.java
* 
	 * @param control
	 * @return observable value
	 * @throws IllegalArgumentException
	 *             if <code>control</code> type is unsupported
	 */
	public static ISWTObservableValue observeSingleSelectionIndex(
			Control control) {
		if (control instanceof Table) {
			return new TableObservableValue((Table) control,
					SWTProperties.SELECTION);
		}
		throw new IllegalArgumentException(
				"Widget [" + control.getClass().getName() + "] is not supported."); 
	}
	/**
	 * @param control
	 * @return an observable value tracking the foreground color of the given
	 *         control
	 */
	public static ISWTObservableValue observeForeground(Control control) {
		return new ControlObservableValue(control, SWTProperties.FOREGROUND);
	}
	/**
	 * @param control
	 * @return an observable value tracking the background color of the given
	 *         control
	 */
	public static ISWTObservableValue observeBackground(Control control) {
		return new ControlObservableValue(control, SWTProperties.BACKGROUND);