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
*             if the property is locked.
	 */
	void setIntervalBase( String intervalBase ) throws ScriptException;
	/**
	 * Returns the interval of this group. The return value is defined in
	 * <code>DesignChoiceConstants</code> and can be one of:
	 * 
	 * <ul>
	 * <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>
	 * 
	 * @return the interval value as a string
	 */
	String getInterval( );
	/**
	 * Returns the interval of this group. The input value is defined in
	 * <code>DesignChoiceConstants</code> and can be one of:
	 * 
	 * <ul>