KTouch: Allow setting required accuracy with more precision

[Sebastian Gottfried]

Hi everyone,

I would like to push one last feature to ktouch/master to close a reported 
wish for KTouch:

https://bugs.kde.org/show_bug.cgi?id=283591

Half the described changes are already there. The only thing missing is 
setting the required accuracy to pass a lesson with one digit precision.

I've now implemented the required changes. The diff for that is very short, 
just 20 lines added, 9 removed. Is it  still okay to push such a small change 
to master? Observing the work on activity support for KDE Edu the Feature 
Freeze is obviously not set in stone.

Best regards,

Sebastian