GZIP compression

This pull-request enables GZIP compression using the GZip filter by James Roper. Future versions of Play will include this filter so that it will no longer require an external dependency.

The GZIP compression only works when the client explicitly accepts compressed data, by specifying this via the Accept-Encoding header. It can be tested for example like this:

    curl -H 'Accept-Encoding: gzip,deflate' http://delving.localhost:9000/organizations/delving/api/search\?query\=\*:\*\&format\=json
Merge pull request #884 from delving/13.04-gzip

Create a now json format that (for example jsonm): minifies the output (strip extra whitespace and hard returns) and gzips it.