Simplify overlay api methods.
New projector view with the current list of speakers.
Merge pull request #1243 from normanjaeckel/ListOfSpeakersView

New projector view with the current list of speakers.
countdown shortcuts
Merge pull request #1230 from ostcar/countdown

Countdown shortcuts
Fixed #1197: Use big heading for custom slides without text.

Keep last projector scale/scroll values after activate new slide.