The AbstractAnnotationItemDelegate is modelled after QAbstractItemDelegate
and should allow consumers of the annotation interfaces to customize the
rendering, the context menu and the tooltip per annotation as wanted.
Yet to be solved:
* whether, and if how, to adapt to zoomed content
* which UI font to recommend if not wanting to use content font
* tooltip hiding API (and perhaps support for async shown tooltips)
and some other TODOs spread over the patch
Done together with some new patches for KDevelop.