Add new top level field "environment"

I propose to add a new top level field named "environment" as discussed here: #143
This field should be reusable because usually it is needed just top level environment for everything but rarely host and app environment can be different.

I propose following fields:
- environment.name
(user-defined environment name like "test", "sandbox", "quality", "production")
- environment.type
(type of this environment like "test", "production")

Examples:
environment.name: sandbox
environment.type: test

environment.name: production
environment.type: production

Maybe there could be also environment.id for env unique identification and environment.kind with values like "onpremise", "cloud".