use routing for file downloads and folder browsing

I started replacing the file download and file browsing links with router generated urls.
@bartv2 please check the download route. I am now always using the files/ajax/download urls which requires a $files parameter and $dir instead of $file

The templates for part.list and part.breadcrumb use the route if it is present for the file but fallback to the old link construction when browsing shared files as a guest.

At the moment I cannot use routing for /core/public.php/, can I? Can we introduce a parameter to the constructor of OC_Route, or how do we do this?

@eMerzh Do you agree that this pull request supersedes #462? If so please comment and close that pull request :)