Desktop notification

Adds support for desktop notifications

![plasma-desktopev2503](https://f.cloud.github.com/assets/48949/512219/7961e5de-be1d-11e2-9844-cdc54c0160e6.png)
![plasma-desktopjy2503](https://f.cloud.github.com/assets/48949/512220/7b25e302-be1d-11e2-81a9-f1c05b24954a.png)