Base images

Currently the following base images are used. Trying to rely on official images as much as possible. - blackfire -> blackfire/blackfire:latest - nginx -> nginx:alpine - percona -> percona:latest - php -> srcoder/development-php:7.0-fpm - php5 -> srcoder/development-php:5.6-fpm - php71 -> srcoder/development-php:7.1-fpm - redis -> redis:alpine - mailhog -> mailhog/mailhog:latest - mytop -> srcoder/mytop:latest - ctop -> wrfly/ctop