move gunicorn configuration from init script to config file

etc/init/pandora.conf

@@ -22,11 +22,5 @@ end script
 
 exec start-stop-daemon \
     --start -c $USER -d $VENV/pandora --exec \
-    $VENV/bin/gunicorn -- \
-       wsgi:application \
-       --bind      127.0.0.1:2620 \
-       --timeout   90 \
-       --max-requests 1000 \
-       -p /var/run/pandora/pandora.pid \
-       --log-level info --log-file /var/log/pandora/pandora.log \
-       --workers   5
+    $VENV/bin/gunicorn -- wsgi:application \
+    -c $VENV/pandora/gunicorn_config.py -p /var/run/pandora/pandora.pid