add docs for affix events

BS3 commits: d9266aee969b2ad57851fffd77409a997ee157d1
fixes 11720 - Add events trigger to affix. fixes 11788 - focusin focusout instead of focus/blur

BS3 commits: c77740bd3abf379ba5880219fc5719eaa0e484d6,
394e0fa6118febbe62ecfb431ab91fff42bdf7d8