packaging: move most of contrib/docker to contrib/packaging/docker contrib/ is kind of a dumping ground for all kinds of random things. Many of the files in contrib/ are related to packaging. But sorting out how everything is related is a lot of effort since it is all mixed together. This commit starts the process of refactoring everything related to packaging so it all lives under one roof. Most content from contrib/docker is simply moved to contrib/packaging/docker and all references are updated. Differential Revision: https://phab.mercurial-scm.org/D3541

FROM debian:__CODENAME__
RUN apt-get update && apt-get install -y \
  build-essential \
  debhelper \
  devscripts \
  dh-python \
  less \
  python \
  python-all-dev \
  python-docutils \
  unzip \
  zip