wizard fixup (#55)

* Retool dockerfile to stick to 3.7 & add maintainer, change wizard to not default always to "app", run when .env exists (like it does in the git tree)

* don't mix up microblog.pub v. micropub

setup_wizard/Dockerfile

@@ -1,5 +1,7 @@
-FROM python:3
+FROM python:3.7
 WORKDIR /app
 ADD . /app
 RUN pip install -r requirements.txt
+LABEL maintainer="t@a4.io"
+LABEL pub.microblog.oneshot=true
 CMD ["python", "wizard.py"]