Slide size on the presenter view should be configurable

[zbenjamin]

On a small screen, the strict next/prev slides are too small to see unless you're very close to the monitor. It would be nice if their size could be customized via command line or config file.

[wunderlich]

I want to support this request. The problem is, that the preview of overlays using beamer-slides is only about 3cm in height -- not readable. Another option would be to show overlays at the "normal" preview place.