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/context/ViewerAttributeBean.java
if ( this.displayTexts == null )
			this.displayTexts = new HashMap( );
		
		String reportConfigName = ParameterAccessor
				.getConfigFileName( this.reportDesignName );
		if ( reportConfigName == null )
			return;
		
		SessionHandle sessionHandle = new DesignEngine( null )
				.newSessionHandle( ULocale.US );
		ReportDesignHandle handle = null;
		try
		{
			
			handle = sessionHandle.openDesign( reportConfigName );
			
			if ( handle != null )
			{
				String displayTextParam = null;
				Iterator configVars = handle.configVariablesIterator( );
				while ( configVars != null && configVars.hasNext( ) )
				{
					ConfigVariableHandle configVar = (ConfigVariableHandle) configVars
							.next( );
					if ( configVar != null && configVar.getName( ) != null )
					{
						String paramName = configVar.getName( );
						Object paramValue = configVar.getValue( );
						
						if ( paramName.toLowerCase( ).startsWith(