Rework user dialog as agnostic

This PR is a rework of the user dialog to make it a bit more agnostic to the rendering technology.

This is a step in order to handle them with qt or webshell in the future.

• A standard command show_dialog was added
• The prompt toolkit modules are not needed anymore to create and show user dialog
  • Internally it still use pt python
• To make sure the user dialog are serializable, it was redesigned based on data classes
  • There is not changes in the actual API

edit_mg was also removed because

• It was not working anymore in bliss 1.11 and no body complains
• menu(mg) was designed for, and is doing a better job