- Unexport Core::Internal::MainWindow and remove its includes.
- Move RssFetcher from Core::Internal to Core.
- Unexport CopyTaskHandler.
- Move TextEditor's completion support and Refactor Overlay
helper classes from TextEditor::Internal to TextEditor as they
are exported.
- Move internal BaseTextBlockSelection into private header.
- Unexport TextEditorOverlay as they are not used.
See BaseTextEditor::setRefactorMarkers(...). The markers support
a clicked signal via BaseTextEditor and tooltips. They feature
a cursor, but are always positioned at the end of the line (not block!).
As special gimmick they do extend the document width when they
are positioned outside the document area.
