[5.4] Added ability to granularly set mailable tries & timeout

[themsaid]

This will allow for something like:

class TestMail extends Mailable implements ShouldQueue
{
    use Queueable, SerializesModels;

    public $tries = 10;

    /**
     * Build the message.
     *
     * @return $this
     */
    public function build()
    {
        return $this->view('mail.newOrder');
    }
}