Use Codacy instead of Landscape (replace badge)

[bittner]

trafficstars

@jezdez I just like to let you know that I requested access for the Codacy app on GitHub on probably the entire jazzband organization. What I intended was just for this repository.

Background: I'm about to phase out the Landscape service for monitoring our code quality and use Codacy instead. I'm also replacing the related badge at the top of the README.

I hope that's fine.

[bittner]

The related change can be seen in https://github.com/jazzband/django-analytical/pull/149/commits/addf53d01c7e1db6916a08bf051613c631ba1b14.