Tour button popover tip should not be targetable when hidden

See https://forum.xwiki.org/t/tour-resume-container-breaks-comment-action-buttons/18211

The tour popover message makes unexpected noise for other use cases.

Proposed solutions:

• set popover-content div to display: none instead of visibility: hidden when hidden
• reduce z-index down from 2000 for tourResumeContainer
• ( delete the popover-content element from DOM when not in use )