Enhanced apps management [WIP]

:construction: 

TODO:
* [ ] merge Handlebars.js pull request which this depends on https://github.com/owncloud/core/pull/10413
* [ ] add »Recommended« tag to recommended apps (directly next to the score)
* [ ] add link to »More apps in the store …«
* [ ] sort by name (in the future by rating + downloads)
* [ ] make it faster!
score should just return an integer and the helper should transform it into an image string. - I can take care of this if you want me to.