Scrollbar fixed

- Added JQuery plugin SlimScroll, so the playlist scrollbar is more in
line with the themes (fixes #13).
- Unfortunatly, SlimScroll does not support easing, while scrolling to a
location, so the animation on "Scroll to current" is deprecated.
- Added a Settings-button, for future implementations, the button is
currently disabled!
- Furthermore, some renaming on the files and refactoring in the file
structure.