D5080: do not add debugger button unless it is meant to be visible

[Aleix Pol Gonzalez]

apol accepted this revision.

REPOSITORY
  R120 Plasma Workspace

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D5080

To: sitter, broulik, bshah, apol
Cc: plasma-devel, progwolff, lesliezhai, ali-mohamed, jensreuterberg, abetts, 
sebas, apol