Update/adapt kreversi docbook to kf5

remove entities kappname, package unused in kf5
remove entity kappversion
replace entity kappname with kreversi
add info how to start demo mode
correct how the game starts
bump date + releaseinfo
remove appendix installation - unused in kf5
remove obsolete comments
update/ new screenshots

Differential Revision: https://phabricator.kde.org/D6635