* agenda_item.get_absolute_url('projector') returns the activate-url of the related slide.
* agenda_item.is_activate() returns True, if the related item is active
* Fixed set_active_slide to accept kwargs
* Reset countdown when saving a new duration time
* Update countdown overlay when begin_speak and end_speak is called
* Fixed blinking countdown
Fixes: #1078, #1076, #1075
* Set a static projector title
* absolute_urls for the activate links
* update the projector when a slide changes (in save())
* insert the absolute_url template filter
* Preview to slides
* renamed is_active to is_active_slide
* The SlideMixin has to come before the PersonMixin
* Update list of speakers
* Render Countdown via JS
* Reconnect projector after connection lost
* Overlays can allways be active and do not appear in the widget
* Rewrote the clock as overlay
