Minor improvments:

Hello,

First of all thank you for your work, I am using this plasmoid every day and it is very useful!

I've made a couple of improvements that you might want to merge:
- fix Raise not being called
- use icons from theme for Play/Pause/Next/Previous buttons
- add a quit button after ``Next``

Here is how it looks on my system (midna plasma theme):
![snapshot2](https://cloud.githubusercontent.com/assets/1681217/4817247/fbd4b274-5ee6-11e4-8c22-ba4745711834.png)