added total queries monitoring

Related with this issue - https://github.com/yiisoft/yii2/issues/2006

config example:

```php
if (YII_ENV_DEV) {
	// configuration adjustments for 'dev' environment
	$config['preload'][] = 'debug';
	$config['modules']['debug'] = [
		'class'		=>	'yii\debug\Module',
		'panels'	=> [
			'db' => [
				'criticalQueriesCount' => 2,
			],
		],
	];
	$config['modules']['gii'] = 'yii\gii\Module';
}
```
Screenshot is below, there is also a title about that query is slow in `a` tag, but it is not seen on the screenshot.

![total_queries_count_screenshot](https://f.cloud.github.com/assets/1748844/2060681/75ef0d76-8c28-11e3-8e44-2edc8a82d4d6.png)