Fix slide change for some presenters

Early release with a basic set of features. Runs stable in tested situations but may crash in other circumstances.

Fixed problems:

• Page up/down were not handled properly. That caused problems with some presenters when changing slides.

Known problems (same as last release):

• Handling display config changes not properly implemented
• Custom layout creation might not work in some situations or has some visual glitches. This feature is still experimental.

Minimum system requirements are OS X 10.8 (Mountain Lion) and has been tested on 10.13.1 (High Sierra). Please let me know about problems and bugs.