Update screenshots and description of examples folder for v0.7.4 

Going through the tutorial with fresh eyes. If this gets merged, we may be able to remove [this file](https://github.com/openframeworks/openFrameworks/blob/master/apps/_Examples_Moved.txt), or at least edit out the [first line](https://github.com/openframeworks/openFrameworks/blob/master/apps/_Examples_Moved.txt#L1)