QuizGame: made compatible with MW 1.21.1.

Changes include, but are not limited to:
* removal of sajax stuff in favor of jQuery + API due to bug #40785 to pre-emptively prevent bitrot
* upload from fixes
* documented i18n messages for translators
* support for 1.19+ logging format
* various other things

Change-Id: Ifa0eb0cad6fd9479c460fb325b08ffab5783297c