Change database config to run of the .env file

Based on an environment that is not Heroku, this would allow users to add in a `.env.*.php`/`.env.php` file to their root project directory to specify database connection details.

Currently, this requires editing the tracked file.

E.g:

<?php

```
return [
	
	'DB_DRIVER'		=> 'mysql',
	'DB_HOST'		=> 'localhost',
	'DB_DATABASE'	=> 'cachet',
	'DB_USERNAME'  	=> 'root',
	'DB_PASSWORD'  	=> 'secret',

];
```