ENH: Replace has_key() for dicts with in operator

The method has_key() for dict objects is deprecated and not supported in Python 3.x. To improve upward compatibility several uses of has_key() on dicts have been replaced with an in operator.

In rare cases these changes may break user programs because some classes allow the use of dict-like objects (e.g. as argument for the constructor). If such objects would be used they now need to be changed to provide the functions required by the operator (like before they needed to provide has_key()).

The file psychopy/preferences/configobj.py was not changed because it is an external library and may be updated later when compatibility with Python 3.x is finally really needed.