xmonad: improve code style

- Follow best practices (check against hlint and scan)
- Move key bindings to separate file
- Add some new keybindings
xmonad: separate media keys
xmonad: add more keybindings

- add searches
- add command runner
xmonad: add keybindings
Merge pull request #1 from terlar/feature/xmonad-cleanup

Feature: XMonad cleanup