improve env.json meta data; add description to config

[bcumming]

• add description field to config.yaml
• add more information about the environment, views, modules, etc to meta/env.json. See below

{
  "description": "An example gcc configuration for CPU-only development",
  "modules": {
    "root": "/user-environment/modules"
  },
  "name": "host-example",
  "views": {
    "default": {
      "activate": "/user-environment/env/default/activate.sh",
      "description": "",
      "root": "/user-environment/env/default"
    },
    "no-python": {
      "activate": "/user-environment/env/no-python/activate.sh",
      "description": "",
      "root": "/user-environment/env/no-python"
    },
    "roots": {
      "activate": "/user-environment/env/roots/activate.sh",
      "description": "",
      "root": "/user-environment/env/roots"
    },
    "run": {
      "activate": "/user-environment/env/run/activate.sh",
      "description": "",
      "root": "/user-environment/env/run"
    }
  }
}

fixes #110