[Feature] Enable experiment modification

[Joshuaalbert]

It's currently impossible to change an experiment once created. However, this is often necessary in evolving situations, e.g. as new data becomes available. We can adopt an opportunistic strategy.

Solution we'd like

• Enable adding new parameters
• Enable changing existing parameters
  Note when a parameter changes, we may not be able to interpret trials anymore. In these cases, these trials remain but get isolated as in violation and do not contribute to analysis. In this case, we need to be able to:
• Count valid trials, instead of len of trial map.
• Be able to determine trial validity, viz determine parameter and parameter value validity.