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
queryString += ( isFirst ? "" : PARAMETER_SEPARATOR ) + name + EQUALS_OPERATOR + paramValue; 
				isFirst = false;
			}
		}
		return queryString;
	}
	/**
	 * Gets the query parameter string with the give name and value.
	 * 
	 * @param paramName
	 * @param value
	 * @return
	 */
	public static String getQueryParameterString( String paramName, String value )
	{
		StringBuffer b = new StringBuffer( );
		b.append( PARAMETER_SEPARATOR );
		b.append( paramName );
		b.append( EQUALS_OPERATOR );
		b.append( value );
		return b.toString( );
	}
	/**
	 * Get report title.
	 * 
	 * @param request
	 *            http request
	 * @return report title
	 */
	public static String getTitle( HttpServletRequest request )