Added support for HTTP Range requests

The current version doesn't support range HTTP requests (http://svn.tools.ietf.org/svn/wg/httpbis/specs/rfc7233.html)

Current behavior : the cached requests doesn't contains response range header and the returned status code is 200. The range header isn't used when generating the cache key. Range : bytes=0:10 and Range : bytes=10:20 are identical for CacheOutput

expected behavior : the filter should return HTTP 206 status code with an appropriate Range header (same as the first request). The cache key should use request range header to generate the key.