Fix: Start Quiz button unhides questionset

[ymdahi]

Addresses #121

• .show() is not adequetly handling unhide event when "Start Quiz" button is clicked.
• The class .hidden never is removed from .questionset, meaning the questions are never displayed.

This patch:

• uses removeClass jQuery method to remove the .hidden class
• removes the .show() method from click and keydown events for .qs-startbutton

Tested on v1.20.11

[otacke]

@ymdahi It seems to be your site's custom stylesheet that is causing the problems.

You're setting .hidden { display: none !important; }. Using !important is a code smell anyway, and here it's preventing jQuery's show() from removing the regular display value. Cmp. https://api.jquery.com/show/