Added clickable Groups list to Sidebar.

This commit adds a list of Groups that a user is a member of to the sidebar, as clickable links to the cred list within that group.  The group listing is displayed under the Tags list.

Note that the heading, Groups, is not a link, unlike Tags, as I couldn't think of anything useful to link it to, which means that the tags header is blue, and the Groups header is black. Personally I don't think this is a major.

I also remembered after committing, that I have also changed the indentation in this section of code, which was 5 spaces, to 4 spaces. Apologies, I probably should have done this in a separate commit, but I got lazy.