Multiple changes: Path selection, songs on startup, cleanup

- Uses Bass/Rhythm/Lead path to select a sensible track on song change
- Opens disk song list on startup from steam folder
- Minor Style cleanup
- Bugfixes, but they might be because I use .Net 4.0

I don't have .Net 4.5 as I haven't touched C# in a couple of years so I've also made a few changes on a Net4.0 branch which I keep rebasing onto master.

I can split into separate pull requests if you only want some of the changes.

![screenshot-p135](https://cloud.githubusercontent.com/assets/1028741/2825296/5529c550-cf48-11e3-8958-0f62837bd2b1.png)