Changing some settings

- Switching from dmenu to j4-dmenu-desktop (and migrate the dmenu
  theming stuff to it)
- Created an script to toggle music and mapping the functionkey to it
- Visually improving the appearance of a focused workspace (Red border +
  background) in the titlebar
Changed the appearance of airline + sorting

- Visual improve the vimrc to be better and faster readable (adding some
comments & headlines)
- Removing the useless "matchit.vim" line which doesn't work proberly and
  does not load the vim-integrated matchit-plugin)
- Changing the airline plugin to display flat tabs not arrow-like stuff
  because it looked ugly and a bit buggy in a small font
- Created a toggle-settings area to quickly (reach) toggle some plugins that
  sometimes are annoying (gitgutter + colorizer + stripwhitespace)
Removing a useless line