WIP: Mechanism for Detector Alignment

[drbenmorgan]

As discussed in PR #1, we need a way to allow for changes to detector alignment from the "ideal" design parameters. At present, the only apparent way to modify the geometry is via hardcoded changes in the config files.

This issue is to start discussion on the use cases and subsequent requirements for such a system

[drbenmorgan]

Just to motivate discussion, here are a few links to tools used in HEP/LHC/Future Colliders software:

• AIDA-2020 [http://aida2020.web.cern.ch/activities/wp3-advanced-software]
  • @pguzowski, that mentions Chris Parkes at Manchester, so perhaps worth chatting to him?
• DD4hep GitHub repo
• LHCb Alignment
• LMGTFY
  • More towards generic detector description, but useful at it throws up quite a bit on that and also integration with things like visualisation, conditions and databases