settings.yml:
* The default URL was unix:///usr/local/searxng-redis/run/redis.sock?db=0
* The default URL is now "false"
The default URL makes the log difficult to deal with:
if the admin didn't install a Redis instance, the logs record a false error.
It worked before because SearXNG initialized the Redis connection when the limiter started.
In this commit, SearXNG initializes Redis in searx/webapp.py
so various components can use Redis without taking care of the initialization step.
