Bug 183919 [Enhancement] add a switch to determine whether to clean viewer image folder when session expires
in current viewer implementation, file in image folder is deleted when its corresponding session expires, could viewer add a switch to allow users to decide whether this deletion operation should be performed.
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/utility/ParameterAccessor.java
/**
	 * Check whether the viewer is used in designer or not.
	 * 
	 * @param request
	 * @return
	 */
	public static boolean isDesigner( HttpServletRequest request )
	{
		boolean isDesigner = false;
		if ( "true".equalsIgnoreCase( getParameter( request, PARAM_DESIGNER ) ) ) 
		{
			isDesigner = true;
		}
		return isDesigner;
	}
	/***************************************************************************
	 * For export data
	 **************************************************************************/
	/**
	 * Check whether the request is to get image.
	 * 
	 * @param request
	 *            http request
	 * @return is get image or not
	 */
	public static boolean isGetImageOperator( HttpServletRequest request )
	{
		String imageName = getParameter( request, PARAM_IMAGEID );
		return imageName != null && imageName.length( ) > 0;
	}