bookmarks: allow deleting active bookmark using '.'

template: add minimal obsfate template function The goal of this series is to have templates capable of displaying the evolution of a changeset in a clean and human-readable way. Add the succsandmarkers template return successors and markers so it can be used separately like this: > {succsandmarkers % "{get(succsandmarkers, "markers")|json};"} The following patches will add template functions that takes successors and markers as inputs and compute various obsfate fields from them.