refactor gnome shell extension

[bonds]

The extension was written by someone that has little experience with Javascript and less with the Gnome libraries. Further, it was hacked together, cargo-culting and copy-pasting until it 'worked'. Variables are named poorly, the code is not organized well, etc. It could use a refactor by someone that knows what they are doing, or, short of that, someone that has a good eye for clean code.

It would neat if Haskell could help somehow, i.e. helping avoid type bugs and such, see related #23.