More extensive server logging

Signed-off-by: Peter Kröner <peter@peterkroener.de>
Some web servers like the static node server don't treat relative urls right if the refering page's url is a directory without a closing slash (eg. `/presentations/Pik`). To help with this we add a closing slash to all paths that need one in the server's directory lising. Additionally let the iframes themselves correct urls if they happen to load one without a slash.

Signed-off-by: Peter Kröner <peter@peterkroener.de>