grilo: Block spotify plugin

Spotify no longer allows unauthenticated coverart access, making the
plugin useless and only print warnings.

Closes #132
3 jobs for wip/mschraal/block-spotify in 20 minutes and 31 seconds (queued for 1 second)
Status Job ID Name Coverage
  Check
passed #4661
pep8

00:04:50

passed #4660
pyflakes

00:04:51

 
  Build
passed #4662
build

00:10:49