support for better integrated ExperimentMetadata and ExperimentConfiguration

[alee]

Omnibus issue dealing with ExperimentMetadata and ExperimentConfigurations / RoundConfigurations:

This is related to how we bootstrap an ExperimentMetadata and its initial set of ExperimentConfiguration / RoundConfigurations.

We need a way to easily add and manage Parameters and ParameterValues to an experiment to handle different treatments, configuration options, etc. Currently very cumbersome to refactor experiments to uncouple treatment types and other parameterizations.

Data migrations may be the simplest choice for this but require in-depth knowledge of the data models which is not ideal.