Improve config file handling

[jmechnich]

Besides my comment about the parentheses in JS files, I have one question: What happens now when someone is trying to access one of the pages in the case that the conf.php is in this particular installation? Can we easily give them some helpful comment what is missing and what they should do to fix it?

Originally posted by @zuphilip in #160 (review)

Configuration file customizations could be handled in a separate file, requires a bit more thought.