Added autostart functionality

This adds autostart functionality to the app. The following things work right now:
- [x] Windows
- [x] GNOME
- [x] KDE
- [x] Unity
- [ ] Mac OS X

I will try to look at the Windows support. Mac OS X will be a bit difficult for me.

Some things to check: 
* Windows support - Maybe @de-code can look at this?
* GNOME support - Maybe @Sietsem can look at this?
* KDE support - Maybe @schoentoon can look at this?

A overall look through the changes would be awesome too.