Create separate package for KDE support

Actually to get snakefire properly running on KDE, user is required to install `python-kde`.

Create a package named `snakefire-kde`:

1. Adding `python-kde4` as dependency
2. Adding `snakefire` to dependencies too.
3. Move file `Snakefire.notifyrc` from `snakefire` package to new package.

And update `README` with instructions for KDE.