LHCb::Track converters
Using small, custom classes in the FastStage is beneficial for speed, but has the downside that the tools (PrChecker, Resolution checker, etc). will not work out of the box.
The idea is to have converters, that convert the custom classes into LHCb::Tracks before the checks are run.
We should agree on a location where to put the code, and on a naming scheme, to keep the messiness under control.