[Console] [ConsoleLogger] added formatOutput method

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | 
I'm not talking about making everything protected but to be able to provide a good extension point covering all possible needs.

If you change your method to the following:

```php
protected function formatOutput($level, $message, array $context = array())
{
    return sprintf('<%1$s>[%2$s] %3$s</%1$s>', $formatLevel, $level, $this->interpolate($message, $context));
}
```

A protected method can access to a private method in the same class.
If some one want a custom display, it can do something like:

```php
class MyConsoleLogger extends ConsoleLogger
{
    protected function formatOutput($level, $message, array $context = array())
    {
        return $message . isset($context['my_specific_key_not_in_message']) ? $context['my_specific_key'] : '';
    }
}
```