Resolver bundles creation + bundles for a bunch of resolvers

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 several resolvers, 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` and the `HACKING.md` file.

**ATTENTION**: since having unlicensed code is a *bad thing* and JS resolvers are at least derivative works of `tomahawk.js`, and possibly also of `QtScriptResolverHelper`, I have taken the liberty of adding a GPL v3 header to those resolvers that had no license. I am aware that it's not ideal to add license statements to code done by people who haven't licensed it explicitly, but I think this choice makes sense, since the alternative is a mess at best and possibly a violation.  I have also added copyright statements for those few resolvers who had none, based on `git blame`.

See https://github.com/tomahawk-player/tomahawk/pull/170 for the Tomahawk part of this pull request.