eggaccelerators pep8 fixes
Simplify Key Grabbing

Bug Ticket: http://bugs.sugarlabs.org/ticket/3412
the code in the egg for grabing the keys had become obsolete
replaced that by GTK3's gtk_accelerator_parse() function

Work done mostly by Jorge Alberto Gómez López (user name: ghost_algorithm)
as a part of Google Code In 2013
Reference: https://www.google-melange.com/gci/task/view/google/gci2013/5704153045139456