Resolver bundles creation + bundles for Subsonic and Ampache

This pull request adds:
* json2desktop.rb, a script that generates metadata.desktop from metadata.json, to be used by Synchrotron;
* makeaxe.rb, a script that reads a resolver's metadata.json and creates a compressed bundle (axe);
* metadata.json files for Subsonic and Ampache, along with needed directory structure changes.

For more information about the metadata.json format and the required directory structure, see the comments in makeaxe.rb.

See https://github.com/tomahawk-player/tomahawk/pull/170 for the Tomahawk part of this pull request.