[Registry-dev] Support for If-Modified-Since header

[Chathura C. Ekanayake]

I have implemented the support for "If-Modified-Since" header in the 
Registry.
Now the registry servlet adds the "Last-Modified" header to all resource 
content responses.
Then the subsequent requests from clients (web browsers, APP client) may 
include
the "If-Modified-Since" header with the last modified value of the 
previous response.

If the date/time specified in the "If-Modified-Since" header is greater 
than or equal to the last modified date/time of the resource,
Registry responds with a "304 Not Modified " response.

If a client does not support caching, it can simply avoid adding the 
"If-Modified-Since" header, in which case
the resource content is always returned in the response.

Thanks,
Chathura