Bug 168172 Add the get() and set() functions of HideDetail parameter on IGroup
Add the get() and set() functions of HideDetail parameter on IGroup, and thus enable the hidedetail shifting on the Group through eventhandler.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/script/element/IGroup.java
*            the sort direction of this group
	 * @throws ScriptException
	 *             if the property is locked or the input value is not one of
	 *             the above.
	 * 
	 */
	void setSortDirection( String direction ) throws ScriptException;
	/**
	 * Checks whether the group header slot is empty.
	 * 
	 * @return true is the header slot is not empty, otherwise, return false.
	 * 
	 */
	boolean hasHeader( );
	/**
	 * Checks whether the group footer slot is empty.
	 * 
	 * @return true is the footer slot is not empty, otherwise, return false.
	 * 
	 */
	boolean hasFooter( );
	/**
	 * Returns the expression evalueated as a table of contents entry for this
	 * item.
	 * 
	 * @return the expression evaluated as a table of contents entry for this
	 *         item
	 * @see #setTocExpression(String)
	 */
	String getTocExpression( );