Add tests for saving and loading each experiments experiment data

[chriseclectic]

What is the expected behavior?

We should add a tests to each experiment that their ExperimentData and AnalysisResult objects can be serialized for saving in DB, and deserialized for loading from DB. These tests shouldn't require access to the cloud DB but just test the serialize functions locally.

[yaelbh]

Note that currently some experiments can be saved and loaded, but not re-analyzed, usually because their analysis requires the experiment to have been serialized saved and loaded. This can be fixed by either serializing and saving the experiment (do we still think we'll want it also for the runtime?), or by checking each usage of experiments in the analysis and trying to figure out a way to overcome the missing experiment.

[yaelbh]

I've assigned all "experiment owners", of existing experiments and of experiments to come (Discriminator, Mitigator, Hahn, T_phi). Note that composite experiments already have these tests, using a mock service.