SwitchList should always open the last data file.

```
Most people using SwitchList will only have one layout file.  Currently, when 
launching SwitchList, it always opens a new empty SwitchList.  Instead, 
SwitchList should open the last layout file.

Workaround for now: double-click on the layout file instead of the program.
```

Original issue reported on code.google.com by `rwbowdi...@gmail.com` on 3 Jan 2013 at 11:44
