URL-Encode password in broker_url

Needed to prevent connection errors if the password contains non-urlsafe characters.

Dockerfile change because all the services using it are mirroring ./ in /app now anyway.
Flower needs because it needs bookwyrm in order to read the celerywyrm config (because flower only allows overwriting broker_url from the command line and we want to do it in Python so we have access to a urlencode function).

celerywyrm/settings.py

@@ -1,10 +1,10 @@
 """ bookwyrm settings and configuration """
 from bookwyrm.settings import *
 
-CELERY_BROKER_URL = env("CELERY_BROKER")
+CELERY_BROKER_URL =  CELERY_BROKER
 CELERY_ACCEPT_CONTENT = ["json"]
 CELERY_TASK_SERIALIZER = "json"
-CELERY_RESULT_BACKEND = "redis"
+FLOWER_PORT = env("FLOWER_PORT")
 
 INSTALLED_APPS = INSTALLED_APPS + [
     "celerywyrm",