Maintaining information on closed evaluators

Closes #763 and might help with #926

  * Added a new collections of closed evaluators to `Evaluators`
  * Added checks in `EvaluatorManager` to ignore messages after it is deemed closed.
  * Tighter locking in `Evaluators` to squash a latent deadlock that got somewhat more probable in this branch

 Additionally, this PR contains two minor changes:

  * Moved `EvaluatorManager.State` to be its own class `EvaluatorState`
  * More protection against slow to shutdown processes in `ProcessContainer`
  * Renamed the `HelloREEFHttp` job to `HelloHTTP`