Major code review, cleaning the code and adding a lot of comments. Also
implements a separate store to keep entities with a reference count and
garbage collection. This closes#15.
Known issues at the moment are:
* Webplayer is no longer working, it has to be refactored.
* AlbumPage is to be implemented.
* Build everything in `public/` folder, to serve only this and avoid
issues with `publicPath` in webpack.
* Moved some icons to FontAwesome and use spinning wheels from
FontAwesome to indicate loading.
* (Very) beginning of a webplayer.
