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
{
	/**
	 * Gets the expression that defines the group. This is normally simply a
	 * reference to a data set column.
	 * 
	 * @return the expression as a string
	 * 
	 * @see #setKeyExpr(String)
	 */
	String getKeyExpr( );
	/**
	 * Sets the group expression.
	 * 
	 * @param expr
	 *            the expression to set
	 * @throws ScriptException
	 *             If the expression is invalid.
	 * 
	 * @see #getKeyExpr()
	 */