Improve JFactory state machine

[nathanwbrei]

This PR redesignes the JFactory state machine, as described in docs/behavior.md, to better enforce a number of guarantees regarding if and when JFactory callbacks get run.

• It fixes bugs:

  • Most importantly, the bug described in issue Exception in JFactory::Init() leads to missing Podio collection #490
  • JEvent::GetCollectionBase() wasn't rethrowing the exception like all the other JEvent getters

• It correctly handles a number of previously unconsidered edge cases

  • Inserting data into a factory after Init() has excepted
  • Inserting() data into a factory on one event, but relying on Process() on another event in the same stream
  • Guaranteeing that Init() doesn't get called if Process() never does

• It changes behavior:

  • Once JFactory::Init excepts, it is never called again. Instead, the exception is stored and re-thrown
  • Once JFactory::Process (and BeginRun, etc) except, it won't be called again until ClearData() is called in preparation for the next JEvent

• It reduces code complexity:

  • The decayed and redundant JFactory::CreationStatus is removed completely
  • Factoring JFactory::InitStatus out from JFactory::Status simplifies logic elsewhere