Simple wrapper for xdg-open functionality. Simply refers
to xdg-open except if there exists mimeo on the system
which it will refer to instead.
So, a simple preference modificator for mimeo over
xdg-open since that is my preference too.
Also gave it a short name so I can do open whenever I
want and don't have to tax my left hand with tying xdg.
Since we now use dotter we can simplify the dir structure for
qutebrowser a lot. Everything dot-filed earlier can now reside
in simple directories called config (for ~/.config/qutebrowser),
data (for ~/.local/share/qutebrowser), and scripts
(for ~/.local/bin) files.