Create containers using the master git branches (#153)

Use the master branches from Gitlab to build development container images.

core/Dockerfile.dev

@@ -0,0 +1,29 @@
+FROM python:3.6-alpine
+
+MAINTAINER Abhilash Raj
+
+#Add startup script to container
+COPY docker-entrypoint.sh /usr/local/bin/
+
+#Install all required packages, add user for executing mailman and set execution
+#rights for startup script
+RUN apk update \
+    && apk add --virtual build-deps gcc python3-dev musl-dev postgresql-dev git \
+    && apk add bash su-exec postgresql-client mysql-client \
+    && pip install -U psycopg2 \
+                      git+https://gitlab.com/mailman/mailman.git?ref=master \
+                      git+https://gitlab.com/mailman/mailman-hyperkitty.git?ref=master \
+                      pymysql \
+    && apk del build-deps \
+    && adduser -S mailman
+
+# Change the working directory.
+WORKDIR /opt/mailman
+
+#Expose the ports for the api (8001) and lmtp (8024)
+EXPOSE 8001 8024
+
+ENV MAILMAN_CONFIG_FILE /etc/mailman.cfg
+
+ENTRYPOINT ["docker-entrypoint.sh"]
+CMD ["master"]