Make several changes in the release and CI setup. (#509)

* Make several changes in the release and CI setup.

- Remove .travis/ directory completely.
- Update deploy.py script to tag with major.minor version
  and remove the v in the tag which it didn't before.
- Fix the CircleCI cron setup.

* Update config.yml

* Use buildkit if possible.

* Use machine executor which supports buildkit.

* Remove setup docker step

* Use newer image.

* Use buildkit syntax for caching pip dependencies.

This should significantly speed up the build process by not having
to build python wheels multiple times.

* Use plain output from buildkit

* Make deploy script work with Python 2.7

Also cache python deps across builds.

* Fix more python3 things

* Install dependency in python3

core/Dockerfile.dev

@@ -1,7 +1,6 @@
+# syntax = docker/dockerfile:1.3
 FROM alpine:3.12
 
-MAINTAINER Abhilash Raj
-
 #Add startup script to container
 COPY docker-entrypoint.sh /usr/local/bin/
 
@@ -12,7 +11,8 @@ ARG MM3_HK_REF
 
 #Install all required packages, add user for executing mailman and set execution
 #rights for startup script
-RUN apk update \
+RUN --mount=type=cache,target=/root/.cache \
+    apk update \
 	&& apk add --no-cache --virtual build-deps gcc python3-dev musl-dev \
    	    postgresql-dev git libffi-dev  \
     && apk add --no-cache bash su-exec postgresql-client mysql-client curl python3 py3-pip linux-headers \