Some reorganization and fixes for recent versions of PsychoPy

The title says it all. I suggest moving some files and folders around to more clearly separate the module `pygaze` from the examples, resources, and miscellaneous files. I also ran into some issues when running `simple_experiment.py`, which I think might be due to my version of PsychoPy (1.78.01). I have fixed these in a bit of an adhoc-way, so more testing will probably be required.