Remove Projects (0) from repo navigation #309

Since GitHub has introduced projects there is this Projects tab on every repo. I am yet to see a repository using them. So I'd suggest removing the tab if there are 0 projects. It would reduce clutter and you will only see it when a repository is actually using projects.

That said I understand why GitHub did it like that - showing it for every repository even though nobody is using it at first - they want people to know about the feature, to open the tab and see the intro copy there. However I think users of Refined GitHub are heavy GitHub users and already know about it.

Implementation should be fairly easy as GitHub already show the number of projects in the tab button.