Lastfm (TopTracks): Port to new spice api

@jagtalon I didnt include the css changes as with #1301, so lmk know your thoughts, comparing this. Also we need a better sign for ~ (it represents listeners, the play button was for playcount). Also should we limit result to 20? or what value?
![toptracks](https://cloud.githubusercontent.com/assets/1424236/5243828/7ee5e294-796a-11e4-81b0-c8588791f781.png)

Don't forget to wrap this in a closure ;)

```
(function(env){
  "use strict";
  env.ddg_spice_lastfm_top_tracks(api_result) {
  ...
}(this)};
```