Move history to own plug-in

[JakobVogelsang]

We are looking through all Mixins of open-scd and want to - step by step - move those into open-scd-core. One of the boundary condition we have for this refactor is to make Mixins SCL independent. With Logging we need to move the items showing the Hitem element into an extra menu type plug-in. As this is core functionality for now, I would suggest making this a showcase plug-in to have this functionality right away delivered with open-scd 2.0.