Update RSS request updated

1. Updated the handler to support both the requests of updating all and
updating some of them.
2. Changed the field of the RSS item in database from 'lastUpdated' to
'lastChecked'.
3. Updated the response to contain not only the url and content of the
updated RSS, but also the name and last-checked time.
4. Updated the way to handle the 'data' socket event so that it can now
handle the request with long length.
5. Updated the client example to show how to send requests of updating
all or some of the RSS.