no longer includes settings slide in presentation.
corrects validation error introduced in commit
b20ec301966b046f5e07cedcd3f9edeef759adb8
updates unit tests
Modifies fade transitions and screen blank with easing curves
backgroundColor setting sets slideMedia to null QString.
If a background colour is set, no slide image/video should be set.
Commands may be executed from slides.
Also, rudimentary command parsing prevents commands starting with su,
sudo, and rm.