Build server and client for environments.
This build server will run inside environment builders and invoke environment-specific scripts for doing builds. It provides a uniform language-independent API for builds to the fission build manager.
The change also includes an implementation of a builder for Python -- this "builder" acts on requirements.txt and runs `pip install` to collect all function deps.
* Add initial support for PHP7
* Update PHP env with now an PSR3 logger (Monolog). Now you can also create a handler function with PSR7 Http message and PSR3 logger in parameter.
* Add examples for PHP7 environement
* For development you can create a function in this path /app/userfuncdev.php it will be loaded
* Switch to alpine base image
* handler now receive an array with request, response and logger object
