Use mod_rewrite to add trailing slash for dirs

[miono]

This is needed since mod_rewrite is executed before mod_dir

If we leave this to mod_dir's DirectorySlash-directive (default on) the redirect will use the protocol the request came in on, which will be http since we terminate SSL in the layer above.

By doing the redirect with a RewriteRule we can include our HTTP/HTTPS handling logic in these redirects aswell.

[miono]

@dainnilsson Can you also merge it, I don't have the permissions...