Core functionality finished

The core functionality of the website is now completed but there are some extra things I would like to add. The first thing is "groups" so that groups of people can privately share bookmarks. This would be useful for organisations or for lecturers that would like to share links with their students. I also need to work on the homepage but it's hard to show exactly what the site can do without somebody logging in and adding their sites, however, some overview of the most popular sites and tags I think will fit in nicely.