Fixed parameter generation and added SQL query helper

Not exactly sure why your parameter generation didn't work for me, but I've added a rather hackinsh solution for now. 

Also added showQuery method that you may want to use. 

Previously all parameters were named p1, because $parameters->containsKey($parameterName) didn't work as intended. 


1. missed public modifier: `public function showQuery`
2. it should get names `getQueryPreview` cause it doesn't show anything, just try to build query preview in very simplified mode without params quoting and etc.