Add support for configuring database prefix

Currently it's not possible to set the database prefix without overriding the config file in the application, it seems like allowing it to be set at the environment level out of the box would be a clean addition, as it's a fairly common requirement.

Author: rossbearman

config/database.php

@@ -54,7 +54,7 @@
 		'sqlite' => [
 			'driver'   => 'sqlite',
 			'database' => storage_path('database.sqlite'),
-			'prefix'   => '',
+			'prefix'   => env('DB_PREFIX', ''),
 		],
 
 		'mysql' => [
@@ -65,7 +65,7 @@
 			'password'  => env('DB_PASSWORD', ''),
 			'charset'   => 'utf8',
 			'collation' => 'utf8_unicode_ci',
-			'prefix'    => '',
+			'prefix'    => env('DB_PREFIX', ''),
 			'timezone'  => '+00:00',
 			'strict'    => false,
 		],
@@ -77,7 +77,7 @@
 			'username' => env('DB_USERNAME', 'forge'),
 			'password' => env('DB_PASSWORD', ''),
 			'charset'  => 'utf8',
-			'prefix'   => '',
+			'prefix'   => env('DB_PREFIX', ''),
 			'schema'   => 'public',
 		],
 
@@ -87,7 +87,7 @@
 			'database' => env('DB_DATABASE', 'forge'),
 			'username' => env('DB_USERNAME', 'forge'),
 			'password' => env('DB_PASSWORD', ''),
-			'prefix'   => '',
+			'prefix'   => env('DB_PREFIX', ''),
 		],
 
 	],