WIP feedback

Implementation based on the original [feedback.js](https://github.com/niklasvh/feedback.js).

[My fork](https://github.com/giokokos/feedback.js) tries to fix some bugs and makes the look and feel more `Bootstrap 3` friendly since the original project is outdated and not maintained anymore. (The overlay is adapted to use the fork)

![inspire - high-energy physics literature database 2](https://cloud.githubusercontent.com/assets/3083746/4659747/9819b12e-5510-11e4-9704-145994597b3b.png)