Bug 136571 Drop property is displayed in Property Editor for all kinds of cells.
Description: Drop property displayed in Property Editor for all kinds of cells. Drop property is only supported by cells in group but it is listed in every kinds of cells even in grid cell which will mislead users.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/SimpleGroupElementHandle.java
/**
	 * The module that provides overall information, especially the command
	 * stack.
	 */
	protected final Module module;
	/**
	 * List of handles to design elements.
	 */
	protected List elements = null;
	/**
	 * Constructs a handle to deal with a list of report elements. The contents
	 * of the given list should be design element handles.
	 * 
	 * @param moduleHandle
	 *            the handle of module
	 * @param elements
	 *            a list of handles of design elements. If a item is not
	 *            <code>DesignElementHandle</code>, it is ignored.
	 * @see DesignElementHandle
	 */
	public SimpleGroupElementHandle( ModuleHandle moduleHandle, List elements )
	{
		assert moduleHandle != null;
		module = moduleHandle.getModule( );
		assert elements != null;
		this.elements = elements;
	}
	/*
	 * (non-Javadoc)
	 *