--> Disabled OK button while instructions are visible.
--> Added Enter and Return keys for submitting an answer.
--> Fixed indentations.
you can commit it once the indent has been made coherent.
should be the same indent as above (or above should be the same indent as here)
committed --> https://cgit.kde.org/gcompris.git/commit/?id=3c58071e736cd4d9b9ce67658c9ca6beaa2bd202