Organize GUI files under the subdirectories

Hi all,

I found synkthing project quite interesting and I've been playing with codebase to get my feet wet and I want to propose small enhancement: organize gui files into subfolders.

![screenshot 2014-08-27 16 16 20](https://cloud.githubusercontent.com/assets/39785/4060212/cf4224b4-2ded-11e4-99ae-efa58f5f37f9.png)
vs
![screenshot 2014-08-27 16 15 54](https://cloud.githubusercontent.com/assets/39785/4060215/d22facd2-2ded-11e4-9826-f2d73e0bbaaf.png)

What do you think?