Slideshow mode

[ferrouswheel]

Having a number of different dashboards is really nice. However, for display purposes it'd be great to be able to put team dashboard into a "dashboard slide show" mode, which would rotate through all (or some subset of) dashboards.

This could probably be implemented in conjunction with #97 - since it determines a periodic refresh, and this would require a periodic change of dashboard.

(Btw appreciate all your work, and all my issue submissions are partly to record what I'd need to do to make team dashboard functional for our own use... and so may submit pull requests in future)