Allow a single config.json file

The idea behind this is to allow for several static environments to be configured in one file. If an env_config.json file exists, it will be used first. If not, check for a config.json and see if it has the key 'env'. If the key exists, use that as the config object. If the key doesn't exist, throw an error.

config.json
```js
{
  "dev": {
    "isDev": true
  },
  "test": {
    "isDev": false,
    "isTest": true
  }
}
```