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
* <li><code>INTERVAL_NONE</code>
	 * <li><code>INTERVAL_PREFIX</code>
	 * <li><code>INTERVAL_YEAR</code>
	 * <li><code>INTERVAL_QUARTER</code>
	 * <li><code>INTERVAL_MONTH</code>
	 * <li><code>INTERVAL_WEEK</code>
	 * <li><code>INTERVAL_DAY</code>
	 * <li><code>INTERVAL_HOUR</code>
	 * <li><code>INTERVAL_MINUTE</code>
	 * <li><code>INTERVAL_SECOND</code>
	 * <li><code>INTERVAL_INTERVAL</code>
	 * 
	 * </ul>
	 * 
	 * @param interval
	 *            the interval value as a string
	 * @throws ScriptException
	 *             if the property is locked or the input value is not one of
	 *             the above.
	 */
	void setInterval( String interval ) throws ScriptException;
	/**
	 * Returns the interval range of this group.
	 * 
	 * @return the interval range value as a double
	 */
	double getIntervalRange( );
	/**
	 * Returns the interval range of this group.
	 *