game: fix issues reported by pylint.

W:112, 8: Attribute '_myturn' defined outside __init__ (attribute-defined-outside-init)
W:  3, 0: Unused import QtWidgets (unused-import)
W:  4, 0: Unused import time (unused-import)
gridWidget: fix issues reported by pylint.

W:163, 0: Bad indentation. Found 16 spaces, expected 12 (bad-indentation)