Changes to Alert class

Sometimes in your application you might have something like this:
- messages is stored in Session::get('message')
- type is stored in Session::get('type')
when you have for example a redirect after a successful/unsuccessful action.

I amended the Alert class and now we can have Alert::message($message)->type($type); instead of having Alert::{$type}($message) which, for me, looks a bit ugly.

Every that worked before still works without any errors.