Draft: First concept of Edm back end

Just showing the code for starting a discussion This is an incomplete (and not yet working) example, but wanted to start discussion before developing too much. This is not supposed to be merged. Many of these files will go to ACTS (ideally)

For now this is only Read-Only classes

Inspired by what is done for tracks and MTJ. There are some implementation differences, possibly driven by misunderstanding on how the acts tracks work The files in the details folder will end up in ACTS.