Changes in `HltEventLoopMgr`:
- `start()` should not be used in the EventLoopMgr as it is executed
  before `prepareForRun`. Moved the relevant code there.
- Also added back calls to `sysBeginRun` (soon to be deprecated) and
  fire the `BeginRun` incident in order to stay in sync with offline.
- Make SORPath configurable via property in `HltEventLoopMgr`
- Store the current "run context" in a private member. This is useful
  for interacting with the IOV(Db)Svc during the start sequence.

Major cleanup of `TrigSORFromPtreeHelper`:
- Inherit from `AthMessaging` to get access to the regular messaging
  macros.
- Use `ATH_CHECK` where it makes sense
- Avoid passing around pointers to the `SOR` object by merging a few
  small methods into one.
- Remove a several `typedef`s and `using` declarations
- Add `eventID` method to create an `EventIDBase` from the RunParams
  ptree.