Merge branch '39-switch-to-alpine-docker-image' into 'master'

Resolve "Switch to Alpine Docker image"

Closes #39

See merge request openappstack/single-sign-on!19

consent_provider/Dockerfile

-FROM python:3.7
+FROM python:3.7-alpine
+
+RUN apk add gcc libc-dev libffi-dev
 
 WORKDIR /usr/src/app
 

login_provider/Dockerfile

-FROM python:3.7
+FROM python:3.7-alpine
+
+RUN apk add gcc libc-dev libffi-dev
 
 WORKDIR /usr/src/app
 

test/login_logout/Dockerfile

-FROM python:3.7
+FROM python:3.7-alpine
 
 WORKDIR /usr/src/app
 

test/login_logout/requirements.txt

 Flask
 Flask-OAuthlib
+Werkzeug==0.16.1 # Due to bug: cannot find url_quote https://stackoverflow.com/questions/60192172/importerror-cannot-import-name-filestorage-from-werkzeug. Can be fixed by migrating from flask-oauthlib to oauthlib.

user-panel @ 1d37f6ec

-Subproject commit b65ce8ad3ee18c2606c8f862f0f87fcb53b4d24b
+Subproject commit 1d37f6ec08d63dce87618213908f07d11f83a51d