Config env variables and instance project file

It is now possible to define a mapping between an env variable and a
config path by defining a json mapping file “App/Config/env.json”.
An third config file as been added (AUTOGEN < PROJECT < INSTANCE) whose
name can also be defined using an environment variable (defaults to
project.instance.json).
Use putenv/getenv instead of less-safe $_ENV
Version freeze in composer
Typo in composer.json
Merge pull request #969 from franckstauffer/env_mapping

Env mapping