Tweak in Lang class

Changed function line() a bit, so we can pass parameters to be parsed by translation. For example:

$this->lang->line('name', 'John');

Where:

$lang['name'] = 'How is %s?';

Result:

'How is John?'
You need to move this right above line 522 ... to spare the lengthy explanations, you should change both lines so that the result is:

    -  Added a second parameter to method ``line()`` to allow passing variables which will be parsed within line string.
    -  Added a third parameter to method ``line()`` to disable error logging for line keys that were not found.