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).

Dockerfile

@@ -9,5 +9,3 @@ WORKDIR /app
 COPY requirements.txt /app/
 RUN pip install -r requirements.txt --no-cache-dir
 RUN apt-get update && apt-get install -y gettext libgettextpo-dev && apt-get clean
-
-COPY ./bookwyrm ./celerywyrm /app/