.htaccess file check added

Like stated in a previous pull request one of the biggest issues while installing Fork is that the .htaccess file doesn't get uploaded, which breaks the url rewriting. When this happens, the user goes to his url and gets redirected to install/ and everything breaks.

This is a check if the .htaccess file exists in the index.php. I implemented a skip for who didn't upload the file on purpose because they use an alternative webserver.