Koenig - Allow heading levels to be changed via markdown expansion
Koenig - Allow heading levels to be changed via markdown expansion

refs https://github.com/TryGhost/Ghost/issues/9623
- disable the default mobiledoc-kit heading text expansion and replace with our own that matches heading markdown at the beginning of existing text and will change the heading level of the existing text

TryGhost/Ghost-Admin,TryGhost/Ghost-Admin,kevinansfield/Ghost-Admin,kevinansfield/Ghost-Admin