adapt kbackup docbook to kf5

remove obsolete comments
remove appendix installation, unused in kf5
remove chapter faq with entities reporting.bugs+updating.documentation, unused in kf5
replace setion help-menu1 with link to fundamentals
improve markup
fix issues reported by http://ebn.kde.org/sanitizer/just-in-time.php
CCMAIL:kollix@aon.at