Add View::composers to register several composers at once

Even when using classes as Composer, when you start to accumulate a lot it can get tedious and unclean to have this kind of things :

```php
View::composer('views', 'Class@method');
View::composer('views', 'Class@method');
View::composer('views', 'Class@method');
View::composer('views', 'Class@method');
View::composer('views', 'Class@method');
View::composer('views', 'Class@method');
View::composer('views', 'Class@method');
```

This pull request simply adds a wrapper shortcut :

```php
View::composers(array(
	'Class@method' => 'view',
	'Class@method' => 'view',
	'Class@method' => 'view',
	'Class@method' => ['view', 'view'],
	// etc.
));
```