Update python_easy_chess_gui.py

* Add feature to interrupt the engine while searching for best move. User can resign, make a new game, adjudicate a game, change mode to neutral, requests engine to move now and exit the app properly.
* Update help.
* Add polyglot book supports. One for the engine and two for the user.

Closes #17
Closes #7
Closes #19

Author: fsmosca