Add support for Guppe groups

[audunmb]

Following Guppe groups can take over your feed, but can be interesting to follow nonetheless. So what if Guppe groups worked in the same way as Hashtags on Elk?

It would work just as followed Hashtags, with it's own place in the sidebar (probably below Hashtags or Lists), and you could click on different groups to get a feed of just that group, just like with Hashtags.