Bug 179931 Provide new interface IStyle to let extension return the style properties values
Provide the IStyle interface to let extension user can return the style property value list for their extension elements.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/extension/IReportItem.java
/**
	 * Gets the list of all the property definitions that the extended element
	 * model has.
	 * 
	 * @return the dynamic property list of the extended element model
	 */
	public IPropertyDefinition[] getPropertyDefinitions( );
	/**
	 * Returns the value of a public property. Returns null if the property is
	 * not defined. If the <code>IReportItemFactory</code> class defines a
	 * property, then this method must accept that property name.
	 * <p>
	 * Property names can be separated with dots and can include array indexes.
	 * For example: barColors[1].pattern. This will occur if a property is
	 * defined as a list or structure.
	 * <p>
	 * If the report element support styles or inheritance, then a return value
	 * of <code>null</code> means that the value should be inherited. BIRT
	 * will use its normal inheritance mechanisms to locate the value. If the
	 * extended element does not support inheritance or styles, then this method
	 * must return the value of each property, including defaults if the value
	 * has not yet been set.
	 * 
	 * @param propName
	 *            the name of the property to get
	 * @return the property value as one of the supported BIRT property types:
	 *         String, Integer, Double, BigDecimal, etc.
	 */
	public Object getProperty( String propName );
	/**