D20209: Add support for KBookmarkOwner to communicate if it has tabs open

[Nathaniel Graham]

ngraham added reviewers: cfeck, dfaure.

REPOSITORY
  R294 KBookmarks

REVISION DETAIL
  https://phabricator.kde.org/D20209

To: hallas, #frameworks, ngraham, cfeck, dfaure
Cc: kde-frameworks-devel, michaelh, ngraham, bruns