Add support for multiple versions of PHP

[rasodu]

Change current dockerfile name:

• phpfpm : 56phpfpm
• phpfpmdev : 56phpfpmdev
• cmd : 56cmd
• php-fpm.conf : 56php-fpm.conf

Create new dockerfiles:

• 70phpfpm
• 70phpfpmdev
• 70cmd
• 70php-fpm.conf

Create docker-compose-70php.overwrite.yml and docker-compose-php70.prod.yml

• This will over write default images used by the phpfpm and cmd service.

New command to run the project.

• docker-compose up -d : start development server with default version of php
• docker-compose -f docker-compose.yml -f docker-compose.prod.yml up -d : start production server with default version of php
• docker-compose -f docker-compose.yml -f docker-compose.override.yml -f docker-compose-php<version>.override.yml up -d : start development server with chosen version of php
• docker-compose -f docker-compose.yml -f docker-compose.prod.yml -f docker-compose-php<version>.prod.yml up -d : start production server with chosen version of php

[rasodu]

Better solution is to use 'PHP_VERSION' variable in the .env file to load different version of dockerfile instead of using additional compose file.

[rasodu]

May not need to create separate docker file cmd service. This file may build as is with php5.6 and php7.0