dockerfile: switch back to the ubuntu:14.04 base image
dockerfile: install ruby2.1 from brightbox/ruby-ng repo
dockerfile: install updated nginx from the nginx/stable repo
dockerfile: keep build and development tools, some gems need to build stuff

Refer #46
init: use linkage to fetch additional mysql access parameters
init: added support for centurylink/mysql and orchardup/mysql images
init: use linkage to fetch additional postgresql access parameters
init: added support for orchardup/postgresql image
init: added support for paintedfox/postgresql image
readme: replace "Internal mysql server" instructions with migration instructions
install: removed internal mysql server
launch a postgresql container if we can connect to the host docker

When the database connection parameters are not specified, the
image will try to spin up a redis container if it is able to
communicate with the host docker.

This is only possible if the following two options are specified in the
docker run command:
  `-v /var/run/docker.sock:/run/docker.sock`
  `-v $(which docker):/bin/docker`

This is primarily added to get the quick start guide to work without
much of a hassle.
init: wait for database server to come online
Merge branch 'remove-internal-mysql'
install: configure unicorn to launch as redmine user
install: configure supervisor to send STOP signal to top unicorn workers
init: autostart all daemons when supervisord is started
Merge branch 'launch-via-supervisord'
readme: utilize the mysql unix socket to login as root
init: remove stale unicorn.pid file