ColorProcessor: addStyle method name is misleading

`addStyle` should be called `setStyle` as invoking the method using existing style as a name is overwriting current value, see
[ColorProcessor::addStyle](https://github.com/joomla-framework/application/blob/master/src/Cli/Output/Processor/ColorProcessor.php#L75)

**Example**
```PHP
$processor = $output->getProcessor();

$processor->addStyle(
	'info',
	new \Joomla\Application\Cli\ColorStyle('red')
);
```
I've marked the `addStyle` method as deprecated, as it's not possible to have multiple styles with same name.