Improve the semantics of pre and post processing functions

[SeanMcOwen]

• Make it more legible
• @danlessa suggested: "MSML note: A somewhat orthogonal thought: does it make sense to us to think about an event-driven approach towards state/param + pre/post processing? This may be a more abstract / general way to approach it. The list of events can be something like OnExperimentCreate, OnExperimentExecute, OnExperimentFinish, OnTrajectoryStart, OnTrajectoryFinish, OnSweepFinish, etc.."
  • on a semantic level
  • event list similar to javascript
  • Almost like MSML protocol
  • Same slots for every experiment